P0500 VSS Fault

[Pappy]

Using Forscan software and a OBDII to USB cable, I have a P1000 code that will not reset and a P0500 VSS code. Speedo works, Cruise works, Tranny shifts, OD turns off/on, No ABS lights, No idiot lights of any kind. I think the P0500 code is preventing the completion of the ""drive cycle". Is the tranny output speed sensor where I should start looking? Or is there a speed sensor on the rear end that might be at fault.

 

[Bedrck47]

P0500 - Vehicle Speed Sensor (VSS) Malfunction Indicates the powertrain control module (PCM) detected an error in the vehicle speed information. Vehicle speed data is received from either the vehicle speed sensor (VSS), transfer case speed sensor (TCSS) or anti-lock brake system (ABS) control module. If the engine rpm is above the torque converter stall speed (automatic transmission) and engine load is high, it can be inferred that the vehicle must be moving. If there is insufficient vehicle speed data input, a malfunction is indicated and a DTC is set. On most vehicle applications the malfunction indicator lamp (MIL) will be triggered when this DTC is set.

• Open in VSS+/VSS- harness circuit.
• Open in TCSS signal or TCSS signal return harness circuit.
• Short to GND in VSS harness circuit.
• Short to GND in TCSS harness circuit.
• Short to PWR in VSS harness circuit.
• Short to PWR in TCSS harness circuit.
• Open or short in the vehicle speed circuit(s) (VSC) between the PCM and appropriate control module.
• Damaged VSS or TCSS.
• Damaged wheel speed sensors.
• Damaged wheel speed sensor harness circuits.
• Damage in module(s) connected to VSC/VSS circuit.
• Damage drive mechanism for VSS or TCSS.

Monitor VSS PID while driving vehicle. This DTC is set when the PCM detects a sudden loss of vehicle speed signal over a period of time. If vehicle speed data is lost, check the source of where the vehicle speed input originates from: VSS, TCSS or ABS. Note: On some MSOF applications, VSS and TCSS PID can be monitor. However if no TCSS PID is available and VSS PID is zero, TCSS circuitry frequency must be checked for loss of sensor signal. If another vehicle electronic module has generated the P0500 and the vehicle does not receive its vehicle speed input from one of the above mention sources (VSS, TCSS or ABS). Check the PCM for Output Shaft Speed Sensor (OSS) DTCs. On OSS applications the PCM uses the OSS to calculated the vehicle speed. If no OSS DTCs are found check for correct PCM configuration. Check PCM configuration for correct tire size and axle ratio.

 

[Pappy]

Something I failed to mention, and I think it's important, is that the code is generated while the vehicle is running and standing still. If I turn the key on but don't crank the engine, clear the codes, turn the key off, turn the key back on (without starting) and connect the scanner, there is no P0500 code. However, if clear the codes, turn the key off, crank the engine - but don't even take it out of "Park", and connect the scanner, I have the P0500 code show up. I read something that said a bad alternator rectifier could cause AC current in the system that confuses the VSS circuits. It seems to me that there are 3 possible issues.
1. An open circuit is detected when not expected. (Broken wire, bad connector, failed sensor)
2. A short is detected. (Less than expected resistance - damaged insulation, failed sensor, stuck relay)
3. Something thinks the truck is moving when it isn't.

Since there are no symptoms, I'd be tempted to ignore the code. BUT, my vehicle inspection/registration is due in Collin County, Texas and I'm pretty sure the P1000 code is going to fail inspection.

Is there an easy way to check the alternator rectifiers without an oscilloscope or physical tear-down?

 

[Pappy]

More info. The P0500 code is generated at start-up ONLY. Key on - not started does not set the code. Start-up then clear codes, drive around, does not set the code. Start up, clear codes, shut down and restart sets the code. I didn't go far enough to reset P1000 drive-cycle code.

 

[Pappy]

I checked the alternator with my multimeter. It is showing about 30 VAC from the alternator terminal to ground and across the battery terminals. I suspect the meter is reading the DC pulses as AC??? Will have alternator checked at parts house.

Unplugged and re plugged two sensors on tranny and one on the rear end. No visible signs of damage. No change. Cleared codes, drove about 50 miles, town and highway (the same path that has historically reset the P1000 code). No luck. I had a driver ride me around so I could monitor "Turbine Shaft Speed", "Output Shaft Speed" and "Vehicle Speed" and sensor fault states. No Trouble Found. The code is now being set when the key is turned on, rather than when engine is started.

Turn key on. Reset codes. Read codes - P1000
Start engine. Read codes - P1000
Drive around. Read codes - P1000
Turn key off.
Turn key on. Read codes - P1000, P0500
Reset codes. Read codes - P1000

===GEM DTC P0500===
Code: P0500 - VSS sensor circuit fault.

Module: Generic Electronic Module

Diagnostic Trouble Code details

VSS sensor circuit fault.

Open VSS circuit.

Shorted VSS circuit.

This DTC may be caused by :

Suspect VSS.

Worn or Damaged VSS drive gear on transmission output shaft.

Suspect PCM.

Faulty or damaged instrument cluster module.

===END GEM DTC P0500===

Any ideas? Why do feel like I'm getting ready to replace the GEM?

 

[stamp11127]

Verify the meter is reading ac correctly by checking one of your house outlets. If it is correct pull the small wire (field) off of the alternator to disable it and see if the code returns after being cleared and a drive cycle.

 

[Pappy]

I took the alternator off and went to have it tested at O'reilly's. They couldn't test it because of a bad adapter??? Since I bought it from them and it has a lifetime warranty,,,. I installed the new alternator. My meter still reads 30VAC - I guess the meter isn't smart enough to know the difference between DC and AC pulsed current. With the alt. completely disconnected - still get the P1000 and P0500 codes. When I disconnect the OSS - I get the same. When I disconnect the sensor on the differential, I get the P1000 and P0500 codes - AND an ABS code - so I think the sensor on the differential is okay. Since the TSS and OSS are the same part, (I think) I'm going to try a new OSS.

 

[Pappy]

I pulled the tranny crossmember support so I could drop the rear end of the tranny enough to replace the OSS. No change. Put the sensor that was in the OSS position in the Turbine speed sensor position. No change. Buckled everything back up. Now I get the P0500 when I turn the key on and when I start the motor, even with the alternator completely disconnected. When the vehicle is driven, the Turbine sensor, output shaft sensor and differential speed sensor all give reasonable readings. This eliminates the possibility of a broken or shorted wire. The fact that the code is created when the key is turned on and when the engine is started, instead of while it is moving, makes me greatly suspicious of the computer.

 

[Bedrck47]

More info. The P0500 code is generated at start-up ONLY. Key on - not started does not set the code. Start-up then clear codes, drive around, does not set the code. Start up, clear codes, shut down and restart sets the code. I didn't go far enough to reset P1000 drive-cycle code.

I would think by now you would have realized that unless you find and fix the problem that is causing P0500 to appear that all you are doing is spinning your wheels, so to speak.


Every time you clear P0500 you are setting P1000 and then you drive around with the hopes that you will complete the drive cycle Then you check the codes and find you have both P1000 and P0500. You then clear the codes and go thru the same cycle over and over.


This will continue to happen until you fix the problem. I posted some information earlier in this thread that was copied from the Ford Service manual that gives causes for the P0500 code. Those causes list the possibility of wiring faults and or sensor faults.


I suggest you obtain a copy of the manual (dvd copy on e-bay $15.00) as there are detailed troubleshooting procedures in the manual about code P0500

 

[Pappy]

http://www.ebay.com/itm/Ford-ALL-Models-2000-2002-Service-Repair-Workshop-Manual-on-DVD-/253126950763?fits=Year:2002|Make:Ford|Model:Expedition&hash=item3aef8abf6b:g:yygAAOSwBahVXVqp&vxp=mtr

Is this the manual you are referring to? Or this one maybe?

http://www.ebay.com/itm/Ford-Family...d=253126950763&_trksid=p2047675.c100005.m1851