The Alchemist
March 28th, 2010, 05:12 PM
Hi, we have got a job at work with an O2 sensor "fault" inherited from a customer who has recently have some hotdog muffs removed from his exh system. The exh flange that was welded is about 1 1/2 inches from the O2 sensors. Vehicle a VT2 GTS 2000.
Initially we thought the O2's had failed (not knowing about the recent welding until later) and I fitted a pair of known good ones that I keep handy and this failed to fix the problem (usual story) so we investigated further.
Unplugging the O2's and measuring the 4 pins with KEY ON , showed 12v on the heater and a good earth on the heater return as expected BUT on the sensor send and return we measured 4.2V on the sensor signal wire and 1.25V on the earth return wire < not correct!
Checking these measurements on a known good car (also in the workshop a VY 2003 R8) showed 0 volts on the sensor send and 0.15V on the earth return > correct. (had to check just in case)
Measuring the wiring at the ECU loom end with the pins removed from the plug showed no back feed from possible wire chafeing through or damage etc ie: no voltage at all. PLugging them back in at the ecu measured the 4.2 and the 1.25V as measured at the O2 sensor plug end. Discussed with customer who mentioned about the welding in passing about 2 weeks ago...which as it happens coincided with the start of the poor running of the engine...
Question: PCM fault from the welding and not unplugging the O2's? Or something else?
Any suggestions or similar experiences welcome.
Regards,
Mike
Initially we thought the O2's had failed (not knowing about the recent welding until later) and I fitted a pair of known good ones that I keep handy and this failed to fix the problem (usual story) so we investigated further.
Unplugging the O2's and measuring the 4 pins with KEY ON , showed 12v on the heater and a good earth on the heater return as expected BUT on the sensor send and return we measured 4.2V on the sensor signal wire and 1.25V on the earth return wire < not correct!
Checking these measurements on a known good car (also in the workshop a VY 2003 R8) showed 0 volts on the sensor send and 0.15V on the earth return > correct. (had to check just in case)
Measuring the wiring at the ECU loom end with the pins removed from the plug showed no back feed from possible wire chafeing through or damage etc ie: no voltage at all. PLugging them back in at the ecu measured the 4.2 and the 1.25V as measured at the O2 sensor plug end. Discussed with customer who mentioned about the welding in passing about 2 weeks ago...which as it happens coincided with the start of the poor running of the engine...
Question: PCM fault from the welding and not unplugging the O2's? Or something else?
Any suggestions or similar experiences welcome.
Regards,
Mike