2005 Pontiac Vibe (Toyota Matrix) tacho issue

This video & question is targetted at any GM/Toyota mechanics or DIY’ers that are familiar with the electrical system on the Vibe or Matrix. If you know someone who fits the above description, please pass it on 🙂

For almost a year now, we have this problem on our 2005 Pontiac Vibe (Same as a Toyota Matrix). It started off with just the crazy tacho that you see in the vid, but has since spread to other systems (May or may not be related to this).

The primary problem is this: When the car is cold and first started up, the tacho will occasionally go wild & crazy for a minute or so. It usually settles down and behaves normally within a minute. Sometimes it doesn’t do it at all (Usually when I am trying to look for the problem).

This tacho behaviour bears no relation to engine behaviour. When this happens, the engine runs normally and smoothly. It is obviously a dodgy connection somewhere between where the tach signal is generated (I assume it’s ‘measured’ correctly by the ECU as the car runs fine) and the gauge. If you turn up the volume, you can ‘hear’ the dodgy connection as it has caused interference which can be heard in the speakers. I guess the problem lays somewhere between the ECU and the dashboard cluster, unless there is a separate sensor on the engine just for the RPM measurement.

In addition to this problem, we have another couple of problems, but I think they could possibly be caused by the ‘interference’ generated by this problem.

Problem 1: “The ClickParty”. If the AC is switched on when you start the car, it often rapidly switches the AC compressor on & off for a few seconds. This causes clicks from the AC compressor clutch engaging and disengaging, along with a decrease in engine RPM when it engages (Normal). This behaviour usually co-insides with the crazy tacho, but sometimes it has happened when there is no crazy tacho. If they are happening together, ‘clickparty’ stops when the crazy tacho stops.

Problem 2: I am getting seemingly random DTC codes set by the computer. I am hopeful that this is a result of crazy tacho interference and will go away when I find the loose connection.

My question to any GM/Toyota mechanics or DIY’ers that are familiar with the electrical system on the Vibe or Matrix. Have you seen this before? Do you have any ideas on which connector would be the most likely ‘culprit’?

I will try the common stuff like power cycling the system, checking the ECU connector etc. I just want to know if anyone knows about this particular quirk before I ‘dive in’.

I have done my due diligence and googled this problem, but found nothing that matched this issue (Yes, there were plenty of tacho issues, but they all seemed more related to engine problems).
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