P1652 code

[Brandon++S]

Getting a P1652 code. Having a high idle issue when coming to a stop with clutch in. Is this the VSS sensor most likely causing the problem?

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[Injuneer]

I looked this one up in the 1996 factory service manual (99% identical to 97). The code is for "VSS Output Circuit". By that it means the PCM VSS data output to the :
- Speedometer
- Cruise Control Module
- Body Control Module
- Radio (97 only)

The diagnostic chart is confusing, but basically deals with the VSS info the PCM is sending to the devices that require vehicle speed input. The first question it asks is "Was the Powertrain On-Board Diagnostic (OBD) System Check Performed?" Appears you did that. Step 2 asks "Does the vehicles speedometer indicate vehicle speed?"

From there it get complicated.

I have never run into this before, and all I can do is refer you to the 1996 FSM, page 6E-794. If you don't have the manual, free download here:

https://www.mediafire.com/?40mfgeoe4ctti

There is a code for the actual VSS = P0500 "Vehicle Speed Sensor Circuit" and that is the one that deals with the VSS and the wiring to the PCM.

[Brandon++S]

Thank you for the reference. Speed on cluster and scanner is spot on. Cruise control is not working, but not sure if this would set code or not. Who knows if scv is working? Car is loud and hard to hear radio anyway. I do have a rpm mismatch of 3 to 500 rpms, not sure if this is related or not. If I clear code it immediately returns just from pulling in the garage. IAC counts are 130 going 30mph not sure if this is normal or not.

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[Injuneer]

The PCM checks the voltage on each of the 4 lines I listed. If the voltage isn’t what it’s supposed to be it sets the code. So the cruise control not working could be setting the code. I was actually going to ask if that was working.

Do you know why the cruise isn’t working? Could be the harness connector at the cruise control module.

Does the radio have a speed-sensitive volume control? Appears that might be something that was only added in 97.

No idea what the VSS input to the body control module is for. Maybe it does something like prevent the rear hatch release from working when the vehicle is moving. The BCM is notorious for cold solder joins on the printed circuit board, might lust be a loose connection.

I can’t think of why the cruise not working, or radio volume control, or anything in the BCM affecting the idle speed. The PCM opens up the IAC valve as RPM increases, to prevent the engine from stalling if the throttle suddenly closes. But that logic is internal to the PCM. If the internal RPM is indicating 500 RPM high, that could cause the RPM to drop slower than it should on decel.

The code description indicates this can be caused by loose connections, and that it may be necessary to remove the dash to access them.

[Brandon++S]

Thank you again. I will address the cruise control not working, didn't realize it wasn't because I never use it. The radio does have the speed control volume, but hard to tell if it's working or not. The scanner or internal rpm is 500 lower than the cluster? Should this be ok? As for as the high idle coming to a stop, I guess I will clean IAC and go from there.

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