Speedo problem

[Rmay]

My speedometer has starting acting strangly - it will all of sudden just drop to zero and stay there. Then it will start crawling up again, registering around 20 when I'm going 60. It will then work normally for awhile, and then stop functioning. Once, a week or so ago, the needle just started jumping all over the dial.

When the speedo dropes to zero, often the power steering drops out at the same time. It will return a few moments later.

I understand that the problem is probably a bad VSS. I know that in the Q this is located on the trannie; I've also been told there is one at the speedo head. Is this so, and is one or the other (which one?) the likely culprit and in need of replacement.

I also had another weird thing happen, and I don't know if they are correlated. The other day the trannie stuck in 3rd gear for about 15 miles. Next time I drove the car - a couple of hours later - the trannie was shifting properly again, and has been since.

[Q451990]

I'd agree that it's the speed sensor since your P/S is droping out... never had this problem, but heard of similar symptoms and the sensor being the solution.

Don't know about the transmission symptoms, but it sort of makes sense... was the speedometer acting up when the transmission wouldn't go into 4th? The service lists the bad sensor as a possible cause for no 3->4 shifts.

Have you tried the self diagnostic for the transmission? A judgment of "2" indicates a problem with sensor, although it shows that it's reading the tail end of the circuit from both sensors... Q45Tech or some of the other members may have more suggestions on which of the sensors is the culprit.

Heath

[Q45tech]

The speedometer board contains the IC which convert the ac signal from the speed sensor to a 0-5VDC signal for meter, PS, and transmission ecu.Check the sensor first for varying frequency at different speeds if ok, then replace speedometer assembly. Service manual has details.

[Q451990]

My service manual indicates that the sensor on the speedometer is a reed switch with a rotating magnetic feild plate that converts the speed in to pulse for the ECU - is that actually within the IC? I guess this is separate from the pulse generated by the speed sensor on the transmission?

I'm not sure I understand why they're generating a second pulse coming out of the instrument cluster for the ECU/TCU.

Just trying to understand this thing so when it breaks on mine I'll be ready...

Heath

[Rmay]

To clarify one point. By being stuck in 3rd gear I didn't mean that it shifted up to 3rd and then wouldn't go into 4th. I meant that it was only in 3rd - it started in 3rd, not in 1st, and didn't shift - up or down - to any other gear.

[Q45tech]

You're not reading your service manual as this [3rd] indicates the transmission is in fail safe----because it is missing a sensor signal!

Terminal #27 on TCU accepts a 0-5VDC signal from the speedomter IC board....are you looking at the pulse to drive the power steering controller?

[DAEDALUS]

I thought the fail-safe put it in 2nd? Regardless, I had that problem once--bad harness connection. But unless you're missing the metal clip that holds the connector on, it's very unlikely, unless you've had some work done recently. I can't remember where exactly the connection is, but it's on top of the engine (very accessible) and, I *think*, near the TB.

[Rmay]

Q45Tech - are you saying that the likely culprit -given the trannie/speedo problems - is the sensor on the speedo head, not the one of the trannie?

Also, I would love to read my service manual - could you indicate the relevant page(s), and I'll have a look.

[Rmay]

If the problem I'm having is with the sensor on the speedo head, I have a few questions:

1. Is this part replaclable w/o replacling the speedo head?

2. What do I need to do to replace it? I presume it is just take a apart the dash, remove the speedo/sensor, replace, replace dash. (I.e. is this a reasonable DIY, or should I take it to a mechanic).

3. After chanding the sensor, does the speedo need to be recalibrated?

[Q45tech]

Look at page AT 43 -50, why are you not using the built in diagnostic setup for AT.

Normally if the speed sensor is putting out some signal voltage then you just change the whole speedo assembly which of course the new one is calibrated [comes with a 0-0 odometer so you have to swap].

[Rmay]

OK, I followed the instructions on EL-43ff for the self-test, but when I turn the trip rest button it does not go into AT check mode - it just displays keeps displaying the miles. (top and bottom, with bottom resting to 0).

What's that about?

[Q45tech]

JWT 1st gear start mods may disable the self check [diagnostic] function of AT [seem to remember that from long ago] will confirm and get back to you. Probably a good idea to use the Consult anyway as you can zero in easier or just substitute a TCU.

Replacing the speedo assembly is more common than replacing the speed sensor by 5 to 1! But the problem usually showed up around 4-5 years and 60-80k on the 90-91-92.

[Professor_Mike]

If you replace the speedo head through the dealer they should be able to call the repair facility and set the odometer.

[Rmay]

But what if I replace the speedo by myself - how then do I set th odometer. (What repair facility would the dealer call?)

[Q451990]

If I remember correctly, back when TJ was at Infiniti of Scottsdale he said he'd have it set for you before shipping... might check with Joe to see if they can still do that.

Heath