CA18DET ECU Signal Ground Pin 30 floating

[vanepico]

Hi Matt et al,

I am attempting to fault find a mate's car with a rather bizzare error. The TPS and coolant temp signal ground pin 30 on the ECU is floating from 5v (in relation to body ground) when the TPS and coolant sensor is plugged in, to 0v when they are disconnected.

It has just occured to me the pin may be not making connection to the ECU which might be causing the problem, but is there any hardware inside the ecu likely to have caused an error here? Does it connect it through the ECU to a ground output pin? Apparently all the wires that go out to the inlet manifold ground (60,50,20,10,116,108 and 107) all have continuity.

Thanks,
Pete

[Matt]

This is a bit of a ECU hardware repair problem. Each ECU is different, but generally the sensor grounds go through a pin and then a track through to other components (or generally the ECU ground)

It may be the case that the track has been burnt through. The only way of really knowing is to open up the ECU and then backtrace the track (where possible) to see where it goes and if it shows continuity (or is burnt out etc)

You could also try connecting the sensor ground to the ECU ground pin and see if that rectifies the issue you are seeing

[vanepico]

Ah yes, you were right.

20200826_185525.jpg

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I have a suspicion it has been caused by the engine earth being on the inlet manifold, without this having a good enough connection to the engine block so a portion of the starter and alternator current will have been going through the signal ground through the TPS and the 5v regulator in the ECU.

I have soldered a 300ma polyfuse over it now, I have no idea how it would react to enough current to melt that pcb track but it's got 2 chances!

[Matt]

At least that was an easy fix. Not the first time I've seen this (with other ECUs)