P1166 DTC - strange voltage

rsxmachine · Post by **rsxmachine** » Sun Oct 28, 2007 8:31 am

just started getting a P1166 error. I started following the troubleshooting procedure in the Helms, the fuses are good, but the voltage between ECU pins A1 & A24 with the ignition on is only between 3-4 volts instead of battery voltage. does this mean the Primary O2 is damaged, or the ECU? I would think since A1 is an output from the ECU it should be at battery voltage regardless? (between A22 & A24 there is normal battery voltage.)

the strange thing is, it came on after I hooked up my laptop to check if the emissions readiness codes were all set because I need to have the state emissions test done. The kal was previously loaded with KManager 1.2.2.2 and my laptop now has 1.2.2.8. I resaved/reuploaded the kal, but still have the CEL and voltage problem. the sensors are stock and I do run a cat so I've never had any emissions-related DTCs before.

Thanks for any help...

rsxmachine · Post by **rsxmachine** » Sun Oct 28, 2007 9:09 am

I just unplugged the primary O2 (the wiring and connector on it still looks perfect), and the voltage is <3v from A1 with the ignition key on :( is my ECU or KPro damaged?

rsxmachine · Post by **rsxmachine** » Sun Oct 28, 2007 9:54 am

I cleared security & reuploaded and the car starts fine but the DTC still comes on within a few seconds and the voltage is still the same. I continued on with the Helms procedure, the voltage between E8 & A24 is zero, and if I disconnect connector E and ground E8 I still don't get battery voltage between A1 & A24 or A1 & body ground. it's about 2.7v with the key on and engine not running or 3.2v with engine running. hmm...

the other thing I tried is changing all 3 fuses mentioned. at this point I can only conclude my ECU is not putting out the proper voltage on A1 to turn on the O2 sensor heater?

ok, here's something else... if I disconnect the A/F sensor relay under the dash, the voltage on A1 goes to zero. I guess I'm confused between what the functions of pins A1 & A22 are

(*edit*) I replaced the sensor and now everything is back to normal... so I guess the Helms procedure for P1166 can be misleading in that it doesn't tell you that the sensor might be bad