Return to the Newsletter Index
iATN Review: Newsletter for Members
First Quarter 2016 EditionWorld's First & Largest Network of Automotive Professionals
Table of Contents
Voltage Drop
Toyota Tundra 4.6 Occasional Smoke
2016 Impala Bi-Fuel CNG/Gas Problems
Greatest Transmission Textbook
Facebook Suggestions
2015 Chevrolet Silverado 6.6L Harness Damage
Dealing with Obsolete Parts
An Unusual Problem

iATN's iOS AppiATN's Android App
Sponsored in part by our Industry Sponsors

As we start off the new year, we'd like to recognize our industry sponsors, and thank them for their continued support of the mission and goals of iATN. The longtime support offered by our corporate sponsors is valued tremendously, and without such strong support, iATN would likely not to have been able to grow and continue to provide support for the industry.

We're also pleased to announce a new way to access iATN via mobile with our new app for iOS. You can read discussions from all areas of iATN, get notifications on interesting discussions, customize your view of the discussions through the menu at the top of the app, and of course, reply to discussions and start new ones with photos and videos. Additionally, premium subscribers can conveniently access the Knowledge Base in order to perform research. The app includes a VIN bar-code scanner for quick vehicle selection.

Download the iATN app in Apple's App Store.

LIVE EVENT: This Friday, March 4 at 12:45pm Central, iATN will broadcast the Vision Exchange panel discussion live via YouTube from the annual VISION Hi-Tech Training and Expo. Automotive service industry professionals (shop owners, managers, educators and industry leaders) come together for an engaging exchange of ideas and initiatives to help build a clear communication path between automotive educators and the industry they serve. This is the time to have your voice heard and be a part of the movement that will strengthen the future of our industry and provide a positive learning path for tomorrow's technicians.

In this edition of the Review we have some really cool discussions to share: a discussion on voltage drop causing fuel trim DTC's, a demonstration of good detective work in locating the root cause of intermittent tailpipe oil smoke, a great heads up on a bi-fuel issue existent on 2016 Chevrolet Impalas, tips from a shop owner about leveraging Facebook for marketing your shop, an old-school suggestion in dealing with obsolete parts, and a GMLAN sleuthing discussion with the GM Data Bus Diagnostic Tool.

We hope you enjoy this edition.

Scott Brown
iATN President

Full Article

Voltage Drop
Technical Tips Forum
Robert from New York

I would like to take a moment to discuss how I was able to efficiently repair a problem vehicle with a simple volt drop test.

The vehicle in question was a 2007 Toyota Sienna. Customer stated started van in am cranked a little longer than normal. It was also beginning to run rough and surge at idle on his way here. Then the check engine light came on. The van stalled but restarted in our parking lot.

I approached the vehicle with scanner in hand. Engine scan revealed codes p0171 p0174 lean both banks. I hit the key it starts right up and idles smooth for a few seconds then the idle becomes unstable and a steady surge sets in. Pressing the throttle causes the surge to disappear and engine seems to run smooth.

So I pull some quick data and see that it is definitely running lean especially at idle. Ok lets do a visual inspection for any missing or broken vacuum or intake components. Some small vacuum lines cracked at vacuum reservoir. Repaired them, restarted still very lean at idle around 20% ltft and 2-8%stft on both banks. It is still trending lean by observing the stft.

Lets look at some more scan data. When the surge occurs I realize that the engine load pid increases dramatically. To me on a Maf car that indicates an increase in flow across the maf. I wondered why the air flow would increase intermittently. I then watched tps pids and realized the throttle was being commanded open. Did some quick graphing and saw that the idle would dip then the throttle would open then the maf and load pids would increase. So all that action was the computer trying to prevent a stall.

On to some fuel system testing. Scope pump looks weak, but not awful. Test pressure and volume found well within specs. Tested fuel quality and found no signs of water or alcohol. Now realizing fuel gauge is on full and it is pretty chilly outside I am wondering if it has a tank full of low volatility summer type fuel in it.

Next I decided to scope injectors. Pattern looked normal for the most part and as the idle dipped the pulse width would increase. So I decided to go for a quick spin up the road and it runs great under load just has a lopy idle.

So testing the fuel delivery system netted no failures. I smoke tested the engine for vacuum leaks and found none. Pinched off brake booster for no change in trims. I tried adding propane externally and watching air fuel sensors and found the did not respond to the external fuel source. I was pretty satisfied it was not a vacuum leak.

Maf tested well within spec at idle and responded quickly and accurately to increases in throttle.

At this point I have just about used up my self alloted hour for diag so I decided to walk away and fix a few other cars and come back to this one later at night when it wasn't so hectic.

Now back to it at night I started to think I either had contaminated injectors, fuel or carbon on valves. I decided to current ramp injectors to to see if I could see a definitive opening point. They actually looked normal. Other than the fact I think it looks like when the pulse width increases the current reduces. That doesn't seem right. If they are on longer then the coil has more time to charge and current should increase slightly until resistance increases, not decrease.

Is it ecm not able to hold a good ground for the injector? I don't think so because looking at the scope pattern it pulls all the way to ground and can keep it there.

Next I voltage drop tested from battery positive to injector positive. At idle it was around 800mv but just before the surge occurred it would increase to 1.3 Volts. There it is! Volt drop tested from battery positive to injector fuse shows no drop! The power goes from ignition switch to injector fuse to injector relay contacts the through the harness to the injectors. I grabbed the relay to pull it out to put my relay tester between fuse box and relay and realized relay was very warm! Installing the relay tester revealed that there was a 800mv-1.3 volt drop across relay contacts! The relay is no good. Installed new relay runs perfect. Tested total current draw across 10 amp injector fuse after repair and it was less than 5 amps so I was sure it was just a bad relay and it hadn't been ruined by excessive current draw.

I hope this long boring read can help someone understand the value of voltage drop testing and how valuable it is to have a firm understanding as to how electricity works.

Wrench on all! Thats it for now.

Full Article

Toyota Tundra 4.6 Occasional Smoke
Technical Tips Forum
Tom from Michigan

This was actually a tech help that I did, and the feedback on the fix made think it might be useful to re-post it here.

2010 Toyota Tundra 4.6 w/60,000 miles, customer recent purchase.

Engine smokes occasionally on start-up, and some when first driving. Seems to happen warm or cold after sitting a bit. Engine runs great except when choking on oil. Then clears out and runs perfect with no smoke at all. Has good even compression, and no blowby. No noises and good oil pressure.

I am 98% sure oil is getting into intake manifold, but I'm not sure where from due lack of familiarity with this engine. I have driven with PCV and breather hoses disconnected to see if any oil was blown out due to excessive crankcase pressure, and after a few hard runs, none was. I suspect oil is being sucked up into PCV system, but PCV inspection or replacement requires intake manifold removal. I'd like know where the PCV draws from and if there are known issues with oil collecting beneath it before I recommend pulling the manifold.

I checked for service bulletins and service info from AllData, and IATN archives. Nothing related found.

Thank You,


Updated on Nov 9, 2015 6:51 AM

I appreciate all the responses so far. Most suggestions are bad valve seals/worn valve guides. Let me give a little more detail. When this truck starts and you drive it, the amount of smoke can be very small, like you might expect with a valve seal issue, all the way up to enough smoke to mimic a very bad head gasket, and it will clear up within a 1/4 mile or less. So at times, it can be A LOT of oil smoke, or very little. But it always clears up and runs clean with no smoke.

Also, I have taken the truck down the road in 2nd gear and tached it up to 4500 and did a hard long decel. This will often show if valve seals are bad. I did this several times with no smoke whatsoever. I'm not saying that's 100% conclusive, but with the amount of smoke I see sometimes, I would expect at least a little puff during this test if it was the seals. I'm not ruling out the seals just yet, but the exact symptoms don't match valve seal issues I have seen over 33 years. However, my lack of familiarity with this engine means anything is possible for now.

I also removed the PCV hose, installed a thin cloth over the intake nipple, and reinstalled the PCV hose. After one start and short drive it was wet with oil, so I'm still fairly convinced that is where it is coming from.

Of all the replies, I was hoping one would describe the location of where the PCV valve sits, and if it is possible for oil to puddle in that area. So if anyone knows that info, I could use it. I would like to rule out the PCV system before going further as that is where my suspicions lie at the moment.

Also, the oil is clean, about 1/2 quart low, (assuming the correct dipstick), and I have no idea of the viscosity except to say it is NOT 90W ;).

FIX posted on Nov 18, 2015 5:44:31 AM

Well, truck is fixed! Most replies were sure it was valve seals. Steve from Tennessee had the great suggestion of installing a pickle jar in the line between the PCV and intake manifold. After just an 8 mile run to town and back there was 2-3 ounces of oil in the jar, so I was convinced I was on the right track with my diagnosis that the oil and smoke was caused by some kind of PCV system problem.

I pulled the intake manifold and then the oil separator where the PCV is mounted and found the problem. The oil separator has 3 holes. One is where the PCV valve goes in, and two vapor entry/oil drain back holes. One at the front and one at the rear of the oil separator. When I pulled the separator, the front drain back pipe that the separator plugs in to was completely stopped up with sludge preventing oil return. This pipe is about 4" long and has two 90* bends, probably making it prone to sludge buildup, so we may see more of these as time goes on. I cleaned the pipe, and replaced the separator and PCV valve. The PCV was also stuck.

I'm not ready to say whether this happened because of lack of maintenance or a design flaw because I have not had anything else apart yet. Right now I'm suspecting a little of both, although clearly this thing hadn't been maintenanced well. But I wouldn't be surprised to see this again in the future on other vehicles because I think the two 90* bends in the front pipe make it prone to buildup.

Full Article

2016 Impala Bi-Fuel CNG/Gas Problems
Technical Tips Forum
James from Florida

This is another post that will only be of use to G.M. technicians at the present time.

If you see a 2015 or 2016 CNG Bi-fuel Impala with a complaint of SES on and will not operate in CNG mode, check for P125D and P01A9 set current.

P125D is for the alternate fuel high pressure system small leak detected and P01A9 is for the alternate fuel rail pressure too high. If you see these codes, command the alternate fuel pressure regulator through the complete range of the control valves. If the up response is not immediate and the down response does not stabilize within 2 seconds, the alternate fuel rail pressure regulator is sticking.

The leak code is due to the high pressure bleeding through the regulator when the vehicle is off, causing a leak detection fault and the increase in rail pressure due to the regulator leak is causing high rail pressure on start up after sitting for a time. This sets the P01A9 code. G.M. is aware of this problem and a recall is forthcoming.

Full Article

Greatest Transmission Textbook
Transmission Forum
Larry from Utah

Here's a link to what is the best transmission textbook I've ever read. It thoroughly covers theory and principles of operation. Copyright date is 2003, but don't let that fool you. All the information is up to date. No dinosaur illustrations or transmission types.

Although the book is out of print, it is still available from Amazon for around $15 used.

The title of the book is Automatic Transmissions and Transaxles 3rd Edition

I purchased the book about 10 years ago when it first came out for $150 and it covers the late model transmissions and the electronic and hydraulic systems that control them in great detail. If you want to know the how and why of what makes an automatic transmission tick, then this is the book for you. []

This book covers torque converters, lockup, valve bodies, computer systems, gear trains, planetaries, and every facet of theory and principles of operation of an automatic transmission you can think of. This book DOES NOT cover rebuilding procedures, per se. It's strictly upper level learning.

This book will be a godsend for those who need to diagnose transmissions, especially those transmissions that don't exactly work as expected after an overhaul or rebuild. This book is for YOU.

Full Article

Facebook Suggestions
Shop Management Forum
Duane from South Dakota

With social media becoming such a big part of our marketing efforts, I thought it would be nice if we shared some ideas and suggestions as to what seems to work best for your shop. I would like to focus on Facebook as it seems to be the most used of all social media sites. To start it off, I will share what I have found.

Pictures are worth a thousand words. It seems that real pictures (i.e. photos taken in your facility rather than stock photos from the net) seem to generate the most interest. I like to use photos of repair jobs that would be intriguing to a lay person such as a cab removed from a ford truck. Anything that catches the eye serves well to keep your name in front of existing customers.

Informative posts such as where to find the correct tire pressure for your vehicle tends to generate the most "shares" which helps get your name in front of potential customers.

When you post to Facebook is just as important as what you post so your post doesn't get lost in the mix of all the other stuff on a persons feed. Facebook has a feature that will allow you to schedule a post to go "live" at a time and date of your choosing. I have found that Saturday afternoon seems to generate the most views however for me, a Monday afternoon post seems to generate fewer "views" but more booked jobs. I assume this is because people may see it on Saturday but by the time my shop opens on Monday it is no longer at the top of their to do list.

Targeting your audience when you "boost" a post is another way of positioning yourself to the correct customers. As an example, I had posting the article from the Washington post not too long ago about the woman who became a mechanic because she felt women were being taken advantage of when it came to auto repairs. I had posted how to prevent this kind of thing like regular maintenance, not choosing a shop based on price and getting a second opinion if needed. I targeted women ages 25-50, that post generated about 15 new customers in 1 week.

For those that don't know, "boosting" a post is simply paying Facebook to put your post out there to people who are not on your friends list. In my opinion it is the best bang for your buck out there for advertising.

What have you found that works? Any tricks you might want to share?

Full Article

2015 Chevrolet Silverado 6.6L Harness Damage
Technical Tips Forum
Martin from British Columbia

Conductor Insulation Rub Through2015 Chevrolet Silverado 2500 HD LT, Transmission Photo
A Product Information Report (PIR) has been submitted identifying the condition described below, that may or may not exist on just this particular truck or others of the same build. A simple repositioning and tightening of a loose cable tie strap, may prevent the need for a subsequent repair on other vehicles.

The vehicle is a 2015 Chevrolet Silverado HD 4WD truck with 6.6L Duramax engine and Allison 6 speed automatic transmission combination. The truck was donated to our program by GM for training and has 10 km accumulated through plant and delivery.

Opening the hood to survey the engine compartment for the first time, the Transmission Control Module (TCM) electrical harness was found to be contacting the serpentine accessory drive belt. [TCM harness to serpentine belt contact] [Harness Chafed]

Further inspection of the harness revealed that the conduit was rubbed through [2015 Chevrolet Silverado 2500 HD LT, Photo] and the insulation was chafed through on one wire in the harness, leaving the conductor bare, but otherwise undamaged. [Conductor Insulation Rub Through]

Looking at the harness routing, the harness runs next to the engine harness at the left front of the engine and should make a high rise upwards before looping down under the upper radiator hose to make connection at the TCM, which is fastened to the radiator fan shroud.

A single cable tie was found loose at the base of where the engine and TCM harnesses are located. [2015 Chevrolet Silverado 2500 HD LT, Transmission Photo]

After repairing the wiring, conduit and re-affixing the label [2015 Chevrolet Silverado 2500 HD LT, Transmission Photo] the original cable tie was re-positioned to maintain the TCM harness securely and routed with sufficient clearance from the drive belt. Moving the cable tie upwards about 3.5" did the job. [2015 Chevrolet Silverado 2500 HD LT, Transmission Photo]

Before fully securing the cable tie, clearance was verified and also that the harness loop to the TCM did not put the TCM connector terminals under stress from being at a too severe angle. Sufficient clearance and routing allows for engine movement without harness damage. [Secure Harness]

With the harness re-positioned and clearance to the drive belt verified [2015 Chevrolet Silverado 2500 HD LT, Transmission Photo] the cable tie was secured and the two harnesses taped together for added security.

Whether this might be an isolated incident or a common concern, if you service customer vehicles with this powertrain set up, it might be worth checking that the TCM harness is properly secured to prevent any need for a subsequent wiring repair.


Full Article

Dealing with Obsolete Parts
Shop Management Forum
Sean from Arizona

I have a Cadillac Allante that got towed to me with an abs problem, and hard brake pedal, that had just left the dealer after $3,000 to repair driveability issues, and they told him that they could not fix the abs system. I investigate how the system works, and find that the abs pump is running, but not pumping. I call around, and it's used, or one NOS on ebay for $695. Cardone used to rebuild it, but quit about ten years ago.

I called him up, and got the ok to open it up, and investigate.There are four small round pieces of plastic that act as check valves inside, and I machined a new one out of aluminum. I then found several plugged passages. Cleaned it out completely, and reassembled with new orings, and this pump now runs like new.

As these vehicles get older, and parts start to become scarce, I think most of us are going to have to get into the fabrication business. I have a good sized Logan lathe, and I use it almost on a daily basis.

Full Article

An Unusual Problem
Technical Discussion Forum
James from Florida

2014 Chevrolet Silverado 1500 LT, ECM/Inputs/Outputs Scan Data2014 Chevrolet Silverado 1500 LT, Waveform
Today, a 2014 Silverado was towed in. The complaint was SES on, power steering inop at times, ABS light on, problems come and go. When I got in the truck, the Service Power Steering message was on, the steering had no assist, the SES and ABS and Brake lights were on. As soon as I moved the truck, the steering worked normally and I drove it inside. From the multiple complaints, it seemed to be a major communication failure. I checked for codes first and saw this....

[2014 Chevrolet Silverado 1500 LT, ECM/Inputs/Outputs Scan Data]

Quite a few codes, huh? Let's see what modules are communicating. Here's the module list on the high speed bus.

[2014 Chevrolet Silverado 1500 LT, ECM/Inputs/Outputs Scan Data]

This vehicle does not have I03 or JL1 so the only modules on the bus not shown are the HMI module and the EBCM. What about Bus activity?

[2014 Chevrolet Silverado 1500 LT, Waveform]

Well, we've got some obvious problems. The HMI is only on the high speed bus but the EBCM is also a gateway module for the HS Expansion Bus. Is this bus active? Let's see....

[2014 Chevrolet Silverado 1500 LT, Waveform]

UGH....nobody home....which modules show on the data list?

[2014 Chevrolet Silverado 1500 LT, Scan Data]

No EBCM here either. I was looking for EBCM communication on GDS2 and could not communicate with the module. I turned the key off and communication was established with both the EBCM and the HMI module for about one minute then they went silent again. I turned the key back on and still no communication. Let's try something. I turned off the key and communications were established again for about one minute. Interesting....I wonder what happens to the HSGMLAN when the key is rotated off. Let's see.

[2014 Chevrolet Silverado 1500 LT, Waveform]

Well, isn't that cute. Normal conditions with the key cycled off. When the modules power down, all communication is lost as expected. What's the next step? Well, there are some clues to look at.

Clue 1 - On the high speed module list, 2 modules are missing but the heading says "Control Module Not Awake."

Clue 2 - There is no communication on the expansion bus as the EBCM is down. Since it acts as the gateway module, the bus cannot communicate without the EBCM.

Clue 3 - The ECM has set U0299-00 High Speed Communication Enable Circuit as current.

Clue 4 - When the key is cycled off, communication is restored and the High Speed Bus waveform returns to normal as all modules are now communicating.

OK, time to use our most important tool between our ears and analyze the failure. Two modules are not communicating and the data tool tells us that they are not awake. The ECM says that a problem exists in the data communication enable circuit. G.M. low speed modules need only a 12 volt spike on the data line to awaken them, but high speed modules are different. They need a dedicated 12 volt enable line from the BCM to awaken. This should be a constant 12 volt feed with the key on, but our modules only awaken with the key cycled off. Why?

How do we find out why this is happening? I went to the data enable circuit for the EBCM and the HMI module at the BCM X4 connector, pin 23. Back-probing the pin, with the key turned on, there is a very short 12 volt spike then no voltage. When the key is turned off, there is a steady 12 volt feed until the BCM powers down as seen on the HSLAN waveform. Pin 22 is the communication enable circuit for the TCCM, ECM, and ATC. Checking this pin, when the key is cycled on, a steady 12 volt output is seen, as expected.

Maybe the signal is being pulled down... unlikely but I can prove it easily. I swapped pin 23 and 22 in the X4 connector. Now, with key on, I have normal communication with the EBCM but no communication with the ECM until the key is turned off. This must therefore be an internal BCM failure. A new BCM solved the problem and everything is fine now.

This shows why, with network communication issues, it's very important not to jump in too quickly. just look for the clues first and analyze the failure before replacing components.

Full Article
Return to the Newsletter Index
Follow iATN's Latest NewsFollow iATN

Like this issue?

Copyright 1995-2017 iATN. All rights reserved. Terms of Use | Privacy Policy | Contact Us