CAN bus diagnostic port problem
#1
CAN bus diagnostic port problem
This is an obscure problem but I thought I'd ask.
The diagnostic port signal on my race car is "dirty". The data signals are erratic (RPM bounces wildly on OBD II monitors). This is a problem because my dash (AiM MXL2) gets RPM, among other things, from this signal.
If I run wires directly from the CAN bus ECU pins to the diagnostic port the data is perfect. But, ABS and power steering are disabled because the ECU is not getting those signals.
I can get RPM signal from elsewhere but I'd rather have the ECU correctly interface with my dash / data acquisition.
Anyone have any ideas other than a new wiring harness? I suppose I could try running new CAN bus wires from the PS and ABS to see if that works.
Alan
The diagnostic port signal on my race car is "dirty". The data signals are erratic (RPM bounces wildly on OBD II monitors). This is a problem because my dash (AiM MXL2) gets RPM, among other things, from this signal.
If I run wires directly from the CAN bus ECU pins to the diagnostic port the data is perfect. But, ABS and power steering are disabled because the ECU is not getting those signals.
I can get RPM signal from elsewhere but I'd rather have the ECU correctly interface with my dash / data acquisition.
Anyone have any ideas other than a new wiring harness? I suppose I could try running new CAN bus wires from the PS and ABS to see if that works.
Alan
#5
The signal is good when the CAN bus harness wires are cut from the ECU connector and I splice wires directly from the ECU CAN bus to the diagnostic connector and/or the Aim.
The above method bypasses ABS and PS. Corresponding error codes show up on my reader as expected.
Alan
#6
No respecter of malarkey
iTrader: (25)
Thanks for the clarification. I have the MXL Pista, but haven’t fully wired it in yet. Have had connector issues using the Cobb Tuning device. The pins in the OE connector are notorious for being loose and loosing the connection. Otherwise I never really saw the specific issue you mention. It was my intention to tap the wires directly to avoid the connector problem though.
Wondering if perhaps you either have a problem in the wiring to the connector port or if maybe you are using something causing a noise interference issue? I know other people haven’t had that issue. Did you try bypassing the connector wiring and tapping directly into the pcm where it feeds those two signals from?
Wondering if perhaps you either have a problem in the wiring to the connector port or if maybe you are using something causing a noise interference issue? I know other people haven’t had that issue. Did you try bypassing the connector wiring and tapping directly into the pcm where it feeds those two signals from?
#7
That's what I suspected. There must be an issue with wiring between the PCM and the port but if you ever trace the wires they are a complex mess. Probably easier to replace the engine bay harness.
Yes (see above). If I tap directly to PCM signal is clean. If the rest of the harness is connected (to acquire PS and ABS) signal is dirty.
AC
Yes (see above). If I tap directly to PCM signal is clean. If the rest of the harness is connected (to acquire PS and ABS) signal is dirty.
AC
#8
No respecter of malarkey
iTrader: (25)
If you refer to the diagram at the wiring end point it lists the pcm connection point information where those two wires originate from. Then just go and tap directly there, essentially replacing/bypassing the harness wiring to the port. If it doesn’t kill those two signals at the diagnostic port then it shouldn’t kill them by eliminating the wiring between there, right?
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Last edited by TeamRX8; 10-10-2017 at 02:59 PM.
#9
If you refer to the diagram at the wiring end point it lists the pcm connection point information where those two wires originate from. Then just go and tap directly there, essentially replacing/bypassing the harness wiring to the port. If it doesn’t kill those two signals at the diagnostic port then it shouldn’t kill them by eliminating the wiring between there, right?
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I'll start shopping for a new harness in the off season. Thanks for the help.
Alan
#10
No respecter of malarkey
iTrader: (25)
Well it doesn’t seem to make sense for the result to be different at the end of a wire than the beginning. Now that I’m looking at the wiring diagram it appears that the ECU signal may split up at a harness connector. I’ll try to look into it further using the electrical diagram book the next time I’m at the shop. The pdf version I have is an early copy and not always reliable.
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Adax (10-15-2017)
#15
Update on this problem.
After a much trouble-shooting it looks like the problem is a bad ABS controller unit. If this it taken out of the circuit PS works and the signal to the AiM dash is clean. AiM dash is equipped with a 120 Ohm terminating resistor for anyone who needs this info.
Will be swapping this out next week.
Thanks again for all the help TeamRX8.
AC
After a much trouble-shooting it looks like the problem is a bad ABS controller unit. If this it taken out of the circuit PS works and the signal to the AiM dash is clean. AiM dash is equipped with a 120 Ohm terminating resistor for anyone who needs this info.
Will be swapping this out next week.
Thanks again for all the help TeamRX8.
AC