Signal Too Low. Permanent Fault

Checking the Signal Cable (-), Front Heated Oxygen Sensor
- Connect the breakout box and check ground terminals.
- Connect engine control module (ECM).
- Ignition ON.
- Connect a voltmeter between breakout box terminals # 33 (# A33) and # 42 (# A42).
- The voltmeter should read approx. 0.7 Volts.

If reading is OK:
^ Proceed to: Checking the Signal Cable (+), Front Heated Oxygen Sensor section below.

If reading is incorrect:
^ Proceed to: Checking Front Heated Oxygen Sensor section below.





Checking Front Heated Oxygen Sensor
- Ignition OFF.
- Disconnect front heated oxygen sensor (HO2S) (blue connector).
- Ignition ON.
- Connect a voltmeter between breakout box terminals # 33 (# A33) and # 42 (# A42).
- The voltmeter should read approx. 0.7 Volts.

If reading is OK:
^ Try a new front heated oxygen sensor.
^ Proceed to: Verification section below.

If reading is incorrect:
^ Proceed to: Checking the Rear Heated Oxygen Sensor section below.





Checking the Rear Heated Oxygen Sensor
- Ignition OFF.
- Front heated oxygen sensor disconnected.
- Disconnect the rear heated oxygen sensor (black connector).
- Ignition ON.
- Connect a voltmeter between breakout box terminals # 33 (# A33) and # 42 (# A42).
- The voltmeter should read approx. 0.7 Volts.

If reading is OK:
^ Try a new rear heated oxygen sensor.
^ Proceed to: Verification section below.

If reading is incorrect:
^ Check cable between front heated oxygen sensor terminal 3 and engine control module # A33 and cable between rear heated oxygen sensor terminal 3 and engine control module # A19 for a short-circuit to ground.
^ Proceed to: Verification section below.





Checking the Signal Cable (+), Front Heated Oxygen Sensor
- Ignition ON.
- Connect a voltmeter between breakout box terminals # 32 (# A32) and # 42 (# A42).
- The voltmeter should read approx. 1.2 Volts.

If reading is OK:
^ Proceed to: Checking Signal Cable (+), Rear Heated Oxygen Sensor section below.

If reading is incorrect:
^ Proceed to: Checking Front Heated Oxygen Sensor section below.





Checking Front Heated Oxygen Sensor
- Ignition OFF.
- Disconnect front heated oxygen sensor (blue connector).
- Ignition ON.
- Connect a voltmeter between breakout box terminals # 32 (# A32) and # 42 (# A42).
- The voltmeter should read approx. 1.2 Volts.

If reading is OK:
^ Try a new front heated oxygen sensor.
^ Proceed to: Verification section below.

If reading is incorrect:
^ Check cable between front heated oxygen sensor terminal 4 and engine control module # A33 for a short-circuit to ground.
^ Proceed to: Verification section below.





Checking Signal Cable (+), Rear Heated Oxygen Sensor
- Ignition OFF.
- Disconnect the rear heated oxygen sensor (black connector).
- Ignition ON.
- Connect a voltmeter between breakout box terminals # 34 (# A34) and # 42 (# A42).
- The voltmeter should read approx. 1.2 Volts.

If reading is OK:
^ Try a new rear heated oxygen sensor.
^ Proceed to: Verification section below.

If reading is incorrect:
^ Check cable between rear heated oxygen sensor terminal 4 and control module # A34 for a short-circuit to ground.
^ Proceed to: Verification section below.





Verification
After carrying out the repair, check that the fault has been remedied as follows:

- Ignition OFF.
- Front and rear heated oxygen sensors connected.
- Engine control module connected.
- Start the engine and idle it.
- Go into diagnostic test menu.
- Watch EFI-153 and EFI-212, wait until the status of EFI-153 and EFI-212 switches to tested. This can take up to 15 minutes after the engine has been started.
- Read diagnostic trouble codes (DTCs). If EFI-153 or EFI-212 are stored they should have intermittent status.

If reading is OK:
^ Fault corrected.

If reading is incorrect:
^ Proceed to: Fault-tracing Information section below.

Fault-tracing Information
The verification result shows that the fault persists.

- Do you want to exit fault-tracing?

Yes:
^ Fault not corrected.

No:
^ Proceed to: Checking the Signal Cable (-), Front Heated Oxygen Sensor section above.