Thermostat Diagnosis Using a Pico Scope
thermostat pico scope 2 thermostat scope 1 thermostat Just finished a diagnosis on a 2002 Saab 9-5 with a 2.0L spark ignition engine. I'm a mobile tech and attended a call out for a check engine light on. Performed a diagnostic scan had a P0117. Customer states vehicle has not over heated. Firstly i started off by checking there was sufficient coolant in the system, and a quick look at some service history shows the system had a flush at a saab dealership approx a year ago. A brief visual inspection of the resivour cap, all looked alright. With the engine cold i performed a pressure test, no leaks found. So out comes my good friend 2 channel Pico scope. Channel A connected to ECT sensor signal wire and channel B connected to ECT ground. As you can see from the waveform attached as the engine reached operating temperature and the thermostat opens a quick rush of cooler coolant flows past the ECT and the voltage momentary increase. In the other waveform i am snapping the throttle and as you can see the voltage rises momentarily which shows good flow, no blockage and good pump circulation. the pico file shows the ground and the high spikes are wear im moving the wiring loom, in which i found bad pin contacts on the ECT sensor itself, So the fix was pretty simple with a small pick bend the pins back, advised the customer may need a new sub loom if code comes back.
Michael from New Zealand
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