Replacing Speedometer Head in '96 J30

[joojoo2915]

Just wondering if anyone had any advice or knew of some place I could find instructions? Is alldata worth getting? I've looked for Haynes manuals and it doesn't appear they have any for the J30. I've also done a search online with minimal luck. Any help would be greatly appreciated. Thanks!

Mike

[metaverse3]

what is the problem ? There might be other solutions, just in case..

[driverdriver]

The whole instrument cluster is replaced as a single part not individual components (i.e. speedometer).

[joojoo2915]

Sorry for the long wait on reply, I wanted to get the package before I started talking again. Got the package today and it is in fact just the speedometer. I purchased the speedometer head because that is what I was told I needed to replace to fix my speed sensor issue that is tripping the check engine light. I will probably pull out the cluster tomorrow and see what I can see, but if anyone has any words of wisdom I could follow I'd be much appreciative. Thank you!

Mike

[metaverse3]

Speed sensor tripping the check engine light is probably the speed sensor. The speedometer is passive and does not trigger any check engine lights. The speed sensor is active inline with the transmission ECU and it will trigger the check engine light..

I doubt if the speedometer will fix the check engine light. Speed sensors are known to go bad on nissan/infiniti's from time to time. I would start troubleshooting there first..

[RobertsnewQ]

Speed sensor tripping the check engine light is probably the speed sensor. The speedometer is passive and does not trigger any check engine lights. The speed sensor is active inline with the transmission ECU and it will trigger the check engine light.

Actually not true. The speed sensor feeds the speedometer FIRST. The speedometer then amplifies the signal and converts it to a constant pulse speed (i.e. correcting for final drive ratio and tire size variations). This signal then travels to the ECU, TCU, steering control unit and body computer (on 94+). The ECU, etc. doesn't care what tire size/final drive ratio the car came with since that is taken care of in the speedo.

I'll assume the OP has done the required diagnosis to check it out.

[metaverse3]

I don't know what I typed wrong for the "not true" statement. I think you misunderstood when I said the speedometer is passive. I meant the speedo is not actively triggering MIL lights.

Faulty speed sensor is always triggered by line signal into ECCS, or slave path, i.e. AT ECU passing the buck to ECCS to trigger signal.

VSS emits pulses. One of the tricks of troubleshooting Speedo issues, and calibration, along with finding valid feed for GPS sensors is to get a direct tap into the vss wire and study voltage rise/fall on a DMM with accelecration/deceleration.

The return path of a VSS wire from speedometer is usually avoided for probably reasons you mentioned. At least, I don't touch them or almost any alarm shop. Installers always try to go for the straight feed from the sensor. Experienced techs will study wire diagrams and go for the line into Speedo.

I don't know if the speedo is intelligent enough with its amplification routine to trigger an MIL light. I do know the ECU's do it.
Modified by metaverse3 at 6:14 PM 7/14/2005

[RobertsnewQ]

Ahhh I see what you mean. I misunderstood your post as saying "actually speedo can't cause MIL" which isn't what you meant. Sorry about the misunderstanding.

In the OPs case I assumed that someone diagnosed it enough to find that the VSS is giving a good signal to the speedo, but that the speedo was passing a bunk signal to the ECU.

I agree that your scenario (bad VSS) is more likely, though.