Join Now
International Automotive Technicians Network
Interlock Fix
Posted to Technical Tips Forum on 7/24/2012 14 Replies

Vehicle will not come out of park at times. I have seen where several posts at iATN and other sites where the person never found the problem and so I am posting my fix here. Some of the suspects involved are the ignition switch, brake switch, meter fuse, Park-No Park switch, Shift-Lock Solenoid, and ground. First tests appear that the shifter shift lock solenoid is bad. We removed the shifter covers and found the solenoid at the bottom and center of the shifter assembly. The shifter releases after using an extension and tapping on the solenoid. The assembly is over $550. We connected a graphing voltmeter (Vantage) to the 2 wires going to the shift-lock solenoid and found no voltage when the shifter is not releasing. We are loosing voltage and not loosing ground. The voltage gets it's hot from a relay. The SHIFT-LOCK RELAY (remember that name) contact side is dependent on a hot from the Brake Switch and the coil side is dependent on a hot from the 10 amp meter fuse. This relay is in the under dash fuse box-body control module behind the glove box. It costs almost $900. There are about 8 mini-relays in this module. All are non replicable and are soldiered into the circuit board. The circuit board is 3 layers thick so the soldier connections are not accessible (easily). Going through he wiring diagrams We tested and found the Blue wire that grounds the coil side of the relay through the park no park switch was working when the problem occurred. So the P-NP switch is OK. We opened up the BCM and plugged it up without its upper and lower covers off. When moving in and out of park I found the relay that was clicking. When the problem occurs we could tap gently the relay and the interlock would release. We ordered a new relay based off the numbers on the relay and images. We removed the old relay by force and cutting off the 5 prongs. Then we soldiered 5 short wires on the remaining terminals on the circuit board. Then we soldiered the relay to the 5 corresponding wires and epoxy the relay to the one next to it. The vehicle is fixed. [2004 Mazda 3 i, Photo] [2004 Mazda 3 i, Photo] [2004 Mazda 3 i, Engine/Propulsion Schematic] [2004 Mazda 3 i, Photo] [2004 Mazda 3 i, Photo] [2004 Mazda 3 i, Photo]

Daniel from Tennessee

Files Referenced:

thumbnail thumbnail thumbnail thumbnail thumbnail thumbnail

14 Replies Received (View Replies)


car Vehicle Data

2004 Mazda 3 i 2.0L

Engine2.0 L
Trans4-speed Automatic (Electronic)