DTC 4-3-5

4-3-5 FRONT HEATED OXYGEN SENSOR TOO SLOW

Preconditions for DTC
^ The ECM continuously monitors the time it takes for the Heated Oxygen Sensor (HO2S) to switch from rich to lean and back to rich again. If this time is too long, the control module interprets this as a fault in the front HO2S and DTC 4-3-5 is set.

Substitute value
^ Fuel trim shut off.

Fault sources
^ Uneven compression.
^ Air leakage in the intake system.
^ Air leakage in the exhaust system.
^ Incorrect fuel pressure.
^ Defective front HO2S.

Fault symptoms
^ May result in poorer performance.

TESTING PROCEDURE





Other DTCs
^ Read off the other DTCs.

If DTC 4-3-6 is stored:
- See: Testing By Trouble Code, DTC 4-3-6 Rear Heated Oxygen Sensor Compensation.
If DTC 4-3-6 is not stored:
- Check the engine compression.





Checking the Compression
^ Carry out a compression test.

If the compression is OK:
- Check for air leakage in the intake system.
If the compression in any cylinder deviates:
- Rectify as necessary.





Checking for Air Leakage in the Intake System
^ Check if there is any air leakage.

If there is no air leakage:
- Check for air leakage in the exhaust system.
If there is air leakage:
- Rectify as necessary.





Checking for Air Leakage in the Exhaust System
^ Check if there is any air leakage.

If there is no air leakage:
- Check the fuel and residual pressure.
If there is air leakage:
- Rectify as necessary.





Checking Fuel and Residual Pressure
^ Check fuel and residual pressure.

If fuel and residual pressure are OK:
- Test with a new front HO2S.
If the fuel or residual pressure are incorrect:
- Rectify as necessary.