Jumping Speedometer & Code U0002

[1SLwLS1]

So my truck has been sitting for about 6 months and after getting it back up and running (8 speed trans swap), the speedometer started jumping around, same with the digital speed displayed on the EVIC.

I have checked all of the wheel sensors, that wiring is good. They all display similar speeds when live scanning in AlfaOBD. The output speed in AlfaOBD doesn't jump around like it does in the dash. I replaced the ABS control module with a used unit and ran an ABS initialization & cleared rolling codes via AlfaOBD but it is still jumping.

I am getting the U0002 from the ABS module (new and old) with Can C Bus Off Performance as the description. From the ECM, I am getting a U1412 Implausible Vehicle Speed Signal Received.

Nothing else seems out of place but it has been sitting a while. The transmission crossmember was welded in place so I suppose some weird voltage could have fried something but I already replaced the ABS control module. I am not really sure where to go from here. Any ideas?

 

[csuder99]

I assume you have a proper PCM for the engine/trans combination. The DTCs point to a communication problem between the ABS module and the PCM. U1412 can set if the speed signal changes too fast but the PCM also compares the speed signal to RPM and the gear the transmission is in. When you say AlfaOBD doesn't jump around are you talking about the individual wheel speed sensors ? That again would indicate the ABS module is working fine but something is getting corrupted from there to the PCM. I haven't checked if there is a data PID in the PCM that shows what it thinks the speed is ? AlfaOBD is kinda slow though so that might not yield definite results.

The ideal tool would be a Picoscope on the CAN bus near the PCM, that's what Ivan from Pine Hollow Auto Diagnostics would do.

 

[1SLwLS1]

I am using the Sound German Automotive harness for the transmission swap, which is using the original PCM modified to an ECM, along with SGA's PCS for TCM and CAN integration.

For clarification of AlfaOBD not jumping around, I am connected to the ABS module within AlfaOBD and am monitoring the data which is smooth while cruising around the neighborhood while the speedometer is jumping. The wheel speed sensors seem within close range at all times and the there is a dataset that specifies output speed and that speed (in km/h) does not jump around nor match the digital speed being displayed in the EVIC (converted to km/h for accurate comparison). Now you state the polling rate is low for AlfaOBD but if I am cruising at a steady speed (steady-ish via Waze GPS), I would think eventually it would align and show a jump, especially since the speedometer jumping increases with speed, e.g. if I am cruising around 20 MPH, the speedometer swings in a 5 MPH range while if I am going 40 MPH, the speedometer swings around in a 10 MPH range (numbers not exact). The speedometer also swings higher than the actual speed, e.g. if I am traveling around 20 MPH, the speedo may swing b/w 25 MPH and 30 MPH.

 

[crackerjack1957]

Maybe check gear ratio in BCM.......most likely not the cause but wouldn't hurt to check.

 

[1SLwLS1]

Talked to Russell (SGA) and he has fixed, there was a delay in the calibration that was messing with the signal causing the issues.