I had this twice during a 3 day off road trip

In both cases I was:

• in low range CDL engaged
• Going down a very steep grade
• ABS activated
• Brakes groaned and screeched a bit as normal after passing through some mud
• In the 1st case it trigger the 3 amigos (cleared with Foxwell) there was a significant water crossing prior
• In the second case I caught the pending code and cleared it no water crossing but a lot of wet snow
• I drove a further 300KM at both low and high speeds (no low range) without issue

I reviewed all the threads on this and found no solutions, the RAVE indicates a possible ground issue.

Has anyone actually had this and corrected it

 

You likely got water or gunk into your wheel hub, or one of the sensor connectors.

I would check all the plugs for the ABS system, and check the wiring over at the sensors for damage or issue


DTC P0501
Vehicle speed sensor signal error Drive cycle B:Signal implausible.

Possible causes by suggested order of priority:
^ Connectors C504, C290, ECM C637 (B).
^ Open circuit - C637/22 (KG) to C504/3 (KG).
^ ABS or Wheel sensor fault.

Connectors C504, C290, ECM C637 (B).
CONNECTOR
^ Check for connector not correctly latched, backed out pins, damaged pins, corroded pins.

Open Circuit - C637/22 (KG) to C504/3 (KG).
OPEN_CIRCUIT
^ Check resistance > 1M Ohm

ABS or Wheel Sensor Fault.
CHECK THE FOLLOWING:
^ Carry out diagnostic checks on the ABS system.
^ Check that ABS system can measure road speed correctly.
^ Check engine speed measured by ABS on road test or rolling road.

Note: The Motronic will not measure road speed if the engine is not running.

POSSIBLE FAULTS
^ Faulty ABS speed sensor or wiring.
^ Faulty ABS ECU.

 

@Llamasayswhat thanks very much

 

@Llamasayswhat I seem to be a bit brain dead today, can you direct me to where you found the troubleshooting flow you posted. I am hoping to go through it later this week, and would like to refer to it and the details for each section.

Thanks very much

 

That is from AllData(I run an auto repair facility and have access to it) You can cross those numbers with the RAVE for the connector locations and wiring breakdowns

You'll need to use the electrical troubleshooting addendum in RAVE for location info for each connector and wiring diagrams

After rereading the diagnostic flow chart, it appears this code sets when 1 wheel speed is off significantly compared to the remaining 3 wheels for 10secs or more, so maybe some serious wheel slip caused your issue?

 

@Llamasayswhat Hmm could be a sticky or dicey caliper both messages were after stops on very steep downhills in low range after ABS kicked in under slow braking so 10 sec plus seems right. That matches your theory of wheel slip if it occurs at slow speed, it could be one caliper is not holding.
I can monitor the sensors with my Foxwell and see if I can duplicate

But thanks very much again, I will update this when I figure it out, so the next guy can start somewhere easy.

 

Just a minor update did all a basic test of all the computers, only one odd thing the SLABs reported slightly lower voltage than the rest about .4 volts 13.5 as to 13.9 during engine running tests. I may have some corrosion in that area.

Wheel sensor test up coming just need a nice empty parking lot, with some gravel.

 

Further update :

Test ABS - braked hard on gravel 3 times nice pedal pulse - no codes
Test T/C punched it in drive 3 times on gravel - no codes
Monitored speed sensors all 4 are working front 2 are the same but 1-2 Mph off the rears only tested to 10 MPH

Hill descent yet to be tested - I may have a bad or going bad Hi/Low detect switch more investigation required

 

Hill descent light stays on properly in the driveway solid green, no chimes. Chimes if I am in Hi range no way to test it there but basic function is good. I have ordered a Hi/Low switch as a backup, mine is suspect, for 50.00 CDN to my door it is cheap enough.

Next up checking all the connectors and local grounds for corrosion as per @Llamasayswhat list, but it has to stop raining for a day or 2.

 

Can I revive this thread? There are a few more out there, but this is the most recent. Did it ever get resolved?

I have this code and have been researching it and the description for P0501 specifically is “VSS Implausible”. Doesn’t this by definition rule out WHEEL speed sensors? Those values are captured by the SLABS and P0501 speaks specifically to the VSS that is above the valve body in the transmission. If there was something wonky with the WSSs, wouldn’t that throw some sort of amigos type code?

And from the Rave:

Vehicle Speed Signal (VSS)
The VSS is used, by the ECM, to control idle speed and overrun cut off. The ECM receives the signal through a hard wired connection direct from the SLABS ECU.
For vehicles fitted with an automatic gearbox, two vehicle speed signals are received by the ECM. The second signal is derived from the main gearbox output shaft speed, and is sent to the ECM by the Electronic Automatic Transmission (EAT) ECU though the Controller Area Network (CAN). The ECM compares the vehicle speed signal generated by the SLABS ECU with that supplied via the CAN.
The ECM also receives transfer box information. This allows the ECM to take in to account the vehicle being driven using low range gearing and compensate as necessary.
On vehicles with manual transmission, the SLABS signal is checked against a threshold value stored in ECM memory. If other engine parameters indicate the engine is at high load and the VSS is below the threshold, a fault condition is registered in the diagnostic memory.
The vehicle speed signal generated by the SLABS ECU is in the form of a pulse width modulated signal (PWM). Pulses are generated at 8000 per mile, and the frequency of the signal changes in accordance with road speed. At zero road speed the ECU outputs a reference signal at a frequency of 2Hz for diagnostic purposes.
Function
The input signal for the SLABS ECU is measured via pin 22 of connector C0637 of the ECM. The SLABS ECU generates a PWM signal switching between 0 and 12 volts at a frequency of 8000 pulses per mile. For vehicles with automatic gearbox the input signal for the EAT ECU is measured via pins 36 and 37 of connector C0637 of the ECM. These pin numbers provide a bi-directional communications link using the CAN data bus.
In the case of a VSS failure on vehicles with automatic gearboxes, the ECM applies default values derived from the EAT ECU. There are no default values for manual gearbox vehicles.
The VSS can fail in the following ways:
- Wiring short circuit to vehicle supply.
- Wiring short circuit to vehicle earth.
- Wiring open circuit.
In the event of a VSS failure, any of the following symptoms may be observed:
- MIL illuminated after 2 driving cycles (NAS only).
- Vehicle speed limiting disabled (manual transmission vehicles only).
- SLABS/HDC warning lamp on and audible warning.

That’s a lot of words. But I am leaning to this having to do with the transfer case being replaced shortly before my purchase. Did they bugger a harness to the T case?