Error P0135 – how to fix?

Code definition P0135

O2 Sensor Heating Circuit Malfunction (Bank 1, Sensor 1)

What does the code P0135 mean

P0135 is a generic OBD-II code indicating that the engine control module (ECM) has tested the O2 sensor heater circuit and detected a problem with the O2 sensor heater circuit in Bank 1.

What causes the code P0135?

• The ECM tests the O2 sensor heater circuit on initial start-up for excessive current draw and a short or open circuit.
• The ECM detects a short circuit, open circuit, or excessive current draw in the glow plug circuit.

What are the symptoms of the P0135 code?

• The ECM will not have any feedback from the O2 sensor until the O2 sensor has given input.
• The engine may run poorly until the exhaust gas is warm enough to activate the O2 sensor and begin to apply an output voltage.
• The Check Engine light will come on to indicate a problem.

How does the mechanic diagnose the P0135 code?

• Visually inspect the electrical connections and wiring harness to the O2 sensor in bank 1.
• Scan the codes and document the data from the frozen frame, then erase the codes to verify the fault.
• Monitors O2 sensor data to verify that the heater circuit is operational
• Checks the O2 sensor connector for proper voltage input from the ECM to the heater circuit.
• Checks the O2 sensor heater circuit for valid resistance as per specification.
• For further diagnostics, spot tests recommended by the manufacturer should be performed.

The most common errors when diagnosing the P0135 code

• Failure to check the O2 wiring harness for water ingress in the wiring harness cover
• O2 sensor not checked for oil or other contaminants
• No new O2 sensor scan to make sure heater circuit is OK
• Replace parts before conducting thorough tests and visual inspections

How serious is the P0135 code?

• The O2 sensors are the fuel control feedback that the ECM needs to properly control the injectors.
• The ECM remains in open loop until the O2 system is repaired or the O2 sensor is restarted.
• An engine stuck in open loop will run very rich, burning more fuel and starting to accumulate carbon.

What repairs can fix the code P0135?

1. O2 sensor replacement
2. Repair or replace O2 sensor wiring or connection.
3. After removing the short circuit, replace the fuse in the heater circuit.

Additional notes regarding code P0135

The O2 sensor heater circuit is used to heat the interior of the O2 sensor to help it report more quickly to the ECM. If the heater fails, the O2 sensor may still provide information to the ECM, but it will take longer than the normal time under two minutes.