DTC 4-3-6

4-3-6 REAR HEATED OXYGEN SENSOR, COMPENSATION

Preconditions for DTC
^ The Rear Heated Oxygen Sensor (HO2S) constantly monitors the front HO2S and its short term fuel trim so that it matches the exhaust gas oxygen content. If the short term fuel trim differs, the rear HO2S makes fine adjustments to it. When this adjustment is excessive, the ECM interprets this as a fault with the front HO2S and DTC 4-3-6 is set.

Substitute value
^ Fuel trim shut off.

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

Fault symptoms
^ May result in poorer performance.

TESTING PROCEDURE





Other DTCs
^ Read off the other DTCs.

If DTC 4-2-5 is stored:
- See: Testing By Trouble Code, DTC 4-2-5 Rear Heated Oxygen Sensor Regulating.
If DTC 4-2-5 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 rear HO2S.
If the fuel or residual pressure are incorrect:
- Rectify as necessary.





Checking the Rear HO2S
^ Switch Ignition ON.
^ Fuel pressure gauge connected.
^ Squeeze the hose between the EVAP valve and the intake manifold with hose pliers P/N 1158957.
^ DTC for the EVAP system can be set.
^ Look up the DTC parameter list.
^ START the engine and let it run at idling speed until the rear HO2S begins operating.
^ The rear HO2S begins operating a short while after the rear HO2S preheating starts.





^ Increase fuel pressure by squeezing the hose after the fuel pressure regulator with hose pliers P/N 1158957.

Voltage across the rear HO2S should rise to approx. 0.8 Volt.

^ Remove the hose pliers.
^ Undo the hose for the combined instrument at the intake manifold.

Voltage across the rear HO2S should drop to approx. 0 Volts.

If the rear HO2S functions as above:
- Test with a new front HO2S.
If the rear HO2S does not function as above:
- Test with a new rear HO2S.