Signal Too Low. Permanent Fault

Checking Power Cable
- Ignition off.
- Disconnect heated oxygen sensor (HO2S) (front heated oxygen sensor: black connector, rear heated oxygen sensor: gray connector).
- Ignition on.
- Connect a voltmeter between heated oxygen sensor connector terminal 1 (main relay 2/32 side) and ground.
- The voltmeter should read battery voltage.

If reading is OK:
^ Proceed to test step below.

If reading is incorrect:
^ Check cable between heated oxygen sensor terminal 1 and main relay (2/32) terminal 3 for an open-circuit.
^ Then proceed to Verification section below.





Checking Signal Cable
- Ignition on.
- Heated oxygen sensor disconnected. Connect a voltmeter between the heated oxygen sensor connector terminal 2 (engine control module (ECM) side) and ground.
- The voltmeter should read approx. 0 Volts.

If reading is OK:
^ Proceed to test step below.

If reading is incorrect:
^ Check cable between heated oxygen sensor terminal 2 and engine control module # A14 (for diagnostic trouble code (DTC) EFI-521)/ # A29 (for diagnostic trouble code EFI-522) for a short-circuit to supply voltage.
^ Then proceed to Verification section below.





Checking Signal Cable Resistance To Ground
- Ignition off.
- Wait for approx. 150 seconds (cars with immobilizer 245 seconds).
- Heated oxygen sensor disconnected.
- Disconnect engine control module.
- Connect an ohmmeter between heated oxygen sensor connector terminal 2 (engine control module side) and ground.
- The ohmmeter should read infinite resistance.

If reading is OK:
^ Proceed to test step below.

If reading is incorrect:
^ Check cable between heated oxygen sensor terminal 2 and engine control module # A14 (for diagnostic trouble code EFI-521)/ # A29 (for diagnostic trouble code EFI-522) for a short-circuit to ground.
^ Then proceed to Verification section below.





Checking Signal Cable Resistance
- Ignition off.
- Heated oxygen sensor disconnected.
- Engine control module disconnected.
- Connect the test box and check ground terminals.
- Connect an ohmmeter between heated oxygen sensor connector terminal 2 (engine control module side) and test box terminal : # 14 (# A14), for diagnostic trouble code EFI-521. # 29(# A29), for diagnostic trouble code EFI-522.
- The ohmmeter should read approx. 0 ohms.

If reading is OK:
^ Proceed to test step below.

If reading is incorrect:
^ Check cable between heated oxygen sensor terminal 2 and engine control module # A14 (for diagnostic trouble code EFI-521)/ # A29 (for diagnostic trouble code EFI-522) for an open-circuit.
^ Then proceed to Verification section below.





Checking Heated Oxygen Sensor
- Ignition off.
- Connect the heated oxygen sensor.
- Engine control module disconnected.
- Connect an ohmmeter between test box terminals # 27 (# A27) and: # 14 (# A14), for diagnostic trouble code EFI-521. # 29 (# A29), for diagnostic trouble code EFI-522.
- The ohmmeter should read 1.5 - 13 ohms.

If reading is OK:
^ The diagnostic trouble code has been caused by poor contact in the rear heated oxygen sensor connector. Check that the pins in the connector are intact.
^ Then proceed to Verification section below.

NOTE: Do not apply rust solvent spray or grease to the heated oxygen sensor (HO2S) connector.

If reading is incorrect:
^ Try a new heated oxygen sensor.
^ Then 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 verification menu.
- Watch the diagnostic trouble code to be verified.
- Wait until its status goes over to tested.
- This can take up to 5 minutes for the EFI-521.
- This can take up to 15 minutes for the EFI-522.
- Read diagnostic trouble codes.
- If EFI-521 or EFI-522 are stored they should have the status of intermittent faults.

If reading is OK:
^ Fault corrected

If reading is incorrect:
^ Proceed to test step below.

Fault-tracing Information
- The verification result shows that the fault persists.
- Do you want to exit fault-tracing?

Yes:
^ Fault not corrected

No:
^ Return to Checking Power Cable section above.