QuestionQUESTION: Hi,
I recently replaced the alternator on my van, and after this the voltage gauge stopped working (no movement at all). I have confirmed that the alternator is working correctly and charging the battery (~14.5V when running), so I'm guessing some contact is bad.
Additionally, the tachometer was previously not working and now it is. I think that supports a bad contact somewhere.
What contacts should I check? Thanks in advance.
ANSWER: Hi Terrance,
The instrument cluster even though mechanical (analog) in appearance has information communicated to it via the digital data bus (a pair of wires) which is centered in the body computer. The bus connects several other modules as well such as the engine and transmission computers. Because there are other gauges and warning lights evidentally functional on your cluster my belief is that the problem with the voltage gauge is in the circuit board of the cluster or the gauge itself. So removal of the cluster and examination of the circuit board traces associated with the volt gauge would be where I would start. The tachometer also was probably a cluster board/gauge interface problem. It would only be an issue of the charging system or the tachometer if there was a simultaneous malfunction that actually affected charging voltage or engine functional problems that were dependent upon the rotational sensors that are the source of the rpm data. In some ways this simplifies the problem. Look at the solder joints between the non-functional gauge(s) and the circuit board.
Roland
---------- FOLLOW-UP ----------
QUESTION: Sorry, reading your reply I remembered something I probably should have mentioned in the question.
When driving, the 'check gauges' light does come on and the chime sounds every now and then, so I assume that means the computer is aware the gauge is at zero.
I have double-checked the connections to the alternator, and perhaps it's relevant to note that when I wiggle the only connection that is not fixed with a nut the tachometer starts jumping. No effect on the voltmeter though.
ANSWER: Hi Terrance,
That additional information suggests that whatever is the oversight of the system voltage, presumably by the bcm or the pcm, that it is not getting an solid reading of that voltage source that it is happy with. I am not certain exactly which pin(s) of the bcm/pcm are the basis for satisfying the voltage criteria. There are obviously several voltage pins that are needed to operate those modules but it is not evident which one might be the basis for the warning chime/check guages. The most obvious candidate is the red/white wire on pin 3 of the pcm which is the 'direct battery voltage' wire. That wire is connected through several splices to the battery and to the output of the alternator, etc. except that a white fusible link is in the pathway (located in the harness of many such links at the rear of the battery). It could be that the white fusible link is blown so check to see if you have 12V on pin 3 of the pcm plug, and if not that is probably why you are getting no volt reading on the gauge and the warnings.
What is the wire color at the alternator that is not fixed with a nut?
Roland
---------- FOLLOW-UP ----------
QUESTION: Hi,
Where would I find the PCM in the car? The wire color at the alternator is black.
AnswerHi Terrance,
The PCM is located on the left inner fender, partially hidden behind the air intake duct (the intake duct helps to cool the PCM). It has a 60-pin connector which has numbers etched to identify the wires.
The 'black' wire at the alternator may actually also show a gray trace? If so, that is the current output wire of the alternator and goes to the battery and is spliced together with all the other wires of the + side of the system including the red/white wire that goes to the PCM where its reading is digitized and sent over the digital data bus to the instrument cluster to produce a reading on the gauge. You would want that to be connected firmly to the alternator.
Roland
