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How many speed sensors are on a 1998 3.2 L V6 2WD? I'm not counting the wheel sensors.

There's the VSS that's on the passenger side towards the tranny rear. This controls tranny shift points? I read that there is another one that controls the speedometer? Perhaps there's two for 4x4s? I replaced the VSS and O-ring a couple of months ago because the speedo was not working. Didn't resolve the problem. I replaced the entire cluster and it has worked fine until a couple of days ago. The speedo is not working again. I'm stumped. :cry:
 

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A 2WD has one VSS, the same sensor controls the speedo, and cruise control (if equipped), with auto transmission installed it also controls the shift points. A 4WD has two sensors because it has a 2:1 Low range transfer case located between the transmission and the rear propeller shaft. The one on the transfer case operates the speedo.
 

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I didnt know 4x4 had 2 of them. I get a CEL for VSS a lot when I off road on loose rocky stuff. I just clear it when I get back to pavement. So far it hasnt caused issues. Now I'm curious which one is actually causing it.

/thread jack
 

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On a 4WD the vehicle speed sensor is located on the transfer case and the transmission speed sensor is located on the extension housing. The CEL & DTC P0502 is a vehicle speed sensor issue.
 

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FFWD 8-years... similar vehicle, same problem, and DTC 0502.
At VSS connector, power and ground are ok. Signal wire has good continuity to meter.
I've just watched YouTube video on testing a 3-wire speed sensor (Hall Effect). Slowly turn, watch voltmeter for pulses. At this point in diagnostic, is that really necessary? If all wiring is good, ... could it be anything else except a bad sensor? Could pulling VSS out and re-seating correct anything?
On a side note, what's triggering a 0502 code? How does the PCM know there's a problem with VSS? They're not connected. ....🤷🏽‍♂️
 

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If the wiring is OK then there is a strong possibility the teeth on the plastic gear that drives the VSS mechanical part is worn out. Btw, the VSS is connected to the PCM as shown in the attached 99 3.2L schematic.
Rectangle Slope Font Parallel Number
 

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Ok. Thanks B. I'm going to pull the VSS and check out that gear. I looked online (Rockauto) to see how these sensors size up. Besides being expensive, seems most images only showed a mating shaft with no replacement gear. What's the SOP for a failed VSS gear? For me, probably another trip to the salvage yard.
Unconfirmed, but I did find that this VSS was well used, so could be lot's of salvage possibilities. From one of the online vendors:
Eye Product Font Art Rectangle


Also, yep, my error on PCM input from VSS. Missed the branch.
Rectangle Slope Font Line Parallel
 

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Automotive tire Finger Household hardware Gas Motor vehicle

Pulled the VSS. The threads had visible sealant on them, so maybe somebody prior had been checking this out. I did notice oil was present in this section (red arrow), which I don't think should be there.
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Automotive tire Wood Gas Gear Automotive wheel system

This was unexpected. I was kind of all set to see the gear come out in pieces or have a half moon section worn out of it. So, I guess this is a good thing.
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Automotive tire Wood Rim Hardwood Electric blue

The drive pin in the sensor came out easily, and it was all pretty oily.
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Pliers Wire stripper Circuit component Electrical wiring Nipper

Since the gear showed good, my focus turned to the sensor.
Just like on YouTube video, hooked up power/ground/voltmeter.
I slowly turned the shaft CCW and could see the pulse (OC), but it was very erratic and the voltage reading at the other times was all over the place; it didn't go back to 12v but rather swung into lots of different values.
As last resort, I grabbed the drill. Mine can run very slowly so I felt confident I wouldn't fry the sensor. Again, ran CCW slow and pulses were now regular but voltage readings were all over the place.
 

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The schematic shows that the VSS output signal in the PCM is connected to a pull-up resistor connected to a DC source. It looks like the VSS may pull the output signal down to ground level and the pull-up circuit pulls it up to +12 to produce a pulse Connect the VSS to the truck wiring and see if there is a difference in the output voltage.
BTW I have seen the VSS electrical part on ebay for as low as 9 bucks.
 

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I hooked up the sensor to vehicle wiring, started vehicle, spun the sensor CCW with cordless drill.
Car Speedometer Gauge Vehicle Trip computer

Just doesn't seem to want to wake up.
Went to salvage yard and recovered two (one for a spare). $5/piece. Also grabbed an oil pressure sending unit as I swapped the instrument cluster (but that's another story).
Before install, I'll hook up the salvage sensor to vehicle wiring and test again with drill (just to be sure).
 

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Ok, so, yeah. I admit it. I fell into the trap of throwing parts at a problem trying to solve it. It just seemed so convenient. VSS drive gear GOOD, wiring was GOOD. Had to be sensor, .... right?
Well, apparently not. Connected both salvage yard sensors to no avail. Still no speedo.
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I did the bench test again with all 3 sensors. While I don't fully understand the readings on the voltmeter, I did observe they were all fairly consistent. Odds of all 3 sensors being bad? Not likely.
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Odds of a bad cluster (bad speedo)? Again, not likely as I have a spare cluster and also no speedo.
Possible, but not probable.
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Stumped.
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Rectangle Slope Font Parallel Technology

However, something curious I discovered. When I had the connectors disconnected (meter, VSS, PCM), all but the Cruise branch, I checked continuity to ground and got a ~.5 ohm value. Certainly not OC. So, I'm thinking it's possible there's something amiss on the Cruise branch.
Could it be providing a ground path, detouring the signal away from the speedo ??? No idea.
Well, that's where I'm headed next anyway.
 

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Fixed it.
De-pinned the wire coming out of H-8 (8) connector, body side, and speedo starts working again. It must have been bleeding off voltage.
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I think I know what happened. On "my" Trooper, the engine side of the H-8 connector is wired for a 1999 Trooper. The body side is wired for a 2000 Trooper. So, I'm guessing Isuzu changed the wiring on this connector between model years. I can't say for sure as the wiring diagrams in my workshop manual becomes very cryptic in 2000.
 

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In a 2000-2002 Trooper 3.5L and Rodeo 3.2L the electric motor operated throttle valve controls vehicle speed, so the Cruise Control feature is built into the PCM.

The 1998 and 1999 3.5L/3.2L engines have a mechanically operated throttle valve so Cruise Control requires additional hardware to control the throttle valve.

This is likely why the VSS wiring is different between the 2000 body wiring harness and the 1999.
 
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