OP_Rover

Hey guys, I need to get my speedo fixed in order to get my inspection. The problem, as I see it, is I get no volt down to the sensor, causing it to fail. I have come to find out that when I unplug the front wiring harness from the ECM, the volts to the VSS return, but obviously the jeep won't run like that. I have replaced the sensor, since it was 1/4 the price of a 4wd one, due to the fact I'm only 2wd (look guys a benefit). I would appreciate if you electrical guys could chime in here, this will be my first major circuit fix. Here are some diagrams:

The wire I'm having trouble with specifically is the brown wire with yellow tracer that runs to prong 2 of the VSS.

Turbo X_J

So you have 5V in the VT/OR when unplugged? Do you have continuity to ground in the brown w/yellow?

OP_Rover

I'm not sure, when I test that tomorrow should I just put the multimeter on continuity and front probe the the prongs? If not how would I go about that...

Radi

Cavity 1 should read 5 Volts DC with the meter set to a low DC Voltage scale and the (-) test lead grounded.

Cavity 2 should read zero ohms with the meter set to a low Resistance range and the (-) test lead grounded.
Don't use the 'continuity' function as they typically call anything less than 20-30 ohms OK. In this application that isn't OK.

CCKen

Couple of questions:

Did your speedometer just suddenly quit, or was it bouncing around then quit?

Have you tried the Instrument Cluster Actuator Test to see if the speedometer on the cluster works?

Has there been any work been done on the transmission?

There shouldn't be any difference between 2WD and 4WD Vehicle Speed Sensors. What part number VSS did you buy that was 1/4 the price of a 4WD VSS? You needed a part number 56027905.

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When you say you unplugged the 'front wiring harness from the ECM', I take it that it was the Black connector on the PCM, which is connector C1.

Connector C1, pin A4 is the ground circuit to the PCM for all the sensors, which are all spliced into a ground network (see schematic below). There is a good possibility that you would see 5 volts on the ground network with engine off and key to RUN. Don't bother trying to check for 5 volts on the Brown/Yellow tracer wire. You need to determine if you have 5 volts at the Violet/Orange tracer wire (pin cav 1).

The VSS gets its 5 volt supply from PCM connector C2 (White), independent from the 5 volt supply to the other sensors (PCM C1 (Black) pin A17).

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Do the IC Actuator Test to see if the Speedometer works. During the test you see the Speedometer needle cycle through, stopping at preset points. If the needle doesn't respond, the instrument cluster must be replaced.

Instrument Cluster Actuator Test

(1) Begin the test with the ignition switch in the Off position.

(2) Depress the trip odometer reset button.

(3) While holding the trip odometer reset button depressed, turn the ignition switch to the On (RUN) position, but do not start the engine.

(4) Release the trip odometer reset button.

(5) The gauges should cycle through their ranges, stopping at intermediate readings, going up and going down, at two second intervals. The indicator lamps should cycle on and off.

(6) The instrument cluster will automatically exit the self-diagnostic mode and return to normal operation at the completion of the test, if the ignition switch is turned to the Off position during the test, or if a vehicle speed message indicating that the vehicle is moving is received from the PCM on the CCD data bus during the test.

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There have been cases where, on 2WD Jeeps, the plastic Speedometer Drive Gear on the transmission output shaft splits and will not turn the Speedometer Pinion gear.

The only way to find out if the plastic Speedometer Drive Gear on the transmission output shaft is split (broken) is to remove the Speedometer Adaptor and look inside the mount hole in the transmission and view the drive gear. If you can't see a split in the drive gear reach in with a flat blade screwdriver and see if you can nudge the gear around the output shaft. If this is not conclusive, you will have to jack the rear wheels off the ground, place the trans in Neutral, and rotate the drive shaft while someone looks at the drive gear.

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Ground Network:

OP_Rover

Yes, I have done the actuator test, and yes it does work, so thankfully I do not need a new cluster, and yes, it would work for some time then quit. However now it is dead 99% of the time. Also, the transmission has not been worked on since I owned it (nor do I believe it ever has been via the vehicles papers).

OP_Rover

The ohms for prong 2 say 3.3 when set on the 200 setting

OP_Rover

Okay, now with the everything plugged in, engine on run and then again while running, prongs one and three read 5.16 volts and two reads .02. However I still have no speedo.

CCKen

Next step is to examine the pinion drive gear on the trans output shaft like I described above.

Edit: You never did explain about the 2WD VSS vs. the 4WD VSS you bought. See above post.

OP_Rover

The deal with that was the guy at the counter asked me if I was rwd or 4wd, I responded 2wd and he said nice choice. The 4wd one was $115, while mine was about $30. However I have found the one he was talking about and it's obviously not what I needed, http://m.advanceautoparts.com/mt/sho...n_jtt_redirect
Yet still called the VSS, however it's obviously not what I needed, and he most likely didn't know what he was talking about.

CCKen

It does get confusing to the uninformed. The Chrysler parts catalogs refer to that as a Vehicle Speed Sensor for some reason. It's a transmision Input and/or Output Speed Sensor. Used on the 1998+ AW4 transmission, either with 2WD or with 4WD. Two required per transmission.

OP_Rover

Right I've heard of it referred to as the "two small transmission speed sensors"

CCKen

Read this thread.

http://www.jeepsunlimited.com/forums...or-Malfunction

Post #18 is the drive gear I was talking about in my previous post, and repeated below.

There have been cases where, on 2WD Jeeps, the plastic Speedometer Drive Gear on the transmission output shaft splits and will not turn the Speedometer Pinion gear.

The only way to find out if the plastic Speedometer Drive Gear on the transmission output shaft is split (broken) is to remove the Speedometer Adaptor and look inside the mount hole in the transmission and view the drive gear. If you can't see a split in the drive gear reach in with a flat blade screwdriver and see if you can nudge the gear around the output shaft. If this is not conclusive, you will have to jack the rear wheels off the ground, place the trans in Neutral, and rotate the drive shaft while someone looks at the drive gear.

OP_Rover

I've seen that thread, thanks for making it easier to find though. That's exactly what I'm going to look for today when I get home from school.

OP_Rover

The gear inside the tranny looks great. However the pinion gear looks, well not like a gear at all.