Meaning of P0135 Generic OBD2 Code
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The technical definition of the P0135 code is: O2 Sensor Heater Circuit Malfunction in Bank 1 Sensor 1
Now that’s quite a mouthful for an OBD2 trouble code, but it actually has a simple meaning. The code is referring to an abnormality in the front oxygen sensor heater circuit in bank 1.
During cold starts, the O2 heater helps the sensor to maintain an accurate reading. If the ECU detects it takes the O2 sensor too much time to react after a cold startup, the check engine light will turn ON and the P0135 code is displayed in the scanner. The normal time for the O2 sensor to react after a cold start is around two minutes. If the heater fails, the vehicle ECU will trigger the check engine light. A Multimeter is a helpful tool to pick up for testing wires and fuses (learn more about fuse testing).
If you’re a visual learner, go ahead and watch this 30 minute video from EricTheCarGuy – he’s troubleshooting a P0141 code which is similar except it’s Bank 1 Sensor 2 (rather than Sensor 1) which would be in the rear. He does an awesome step-by-step guide to troubleshooting the O2 sensor.
What are the causes of P0135 OBD-II Code?
This generic DTC code is caused by a short or open circuit in the O2 sensor heater. Inevitably, it also means the ECU is detecting excessive current in the O2 sensor heater circuit. This can mean the resistance in the O2 heater element or circuit is high, or there is a short or open circuit in the wiring harness of the O2 sensor.
- Failed or corroded O2 sensor
- Blown Fuse
What are the symptoms of P0135 DTC?
With a P0135 fault, the ECU will not have O2 sensor feedback until the exhaust is hot enough. This means the system will continue running in open loop until the problem is fixed. With that being said, the check engine light is usually accompanied by an extra rich burn which results in poor fuel economy, excessive carbon buildup, and strong exhaust fumes. After fixing the O2 sensor, the A/F (air fuel) ratio should return to normal and fix any sort of ghost issues.
- Check Engine Light illuminated
- Rough Idle
You can also expect the engine to have idling problems with a P0135 generic OBD2 code, most especially if the motor is cold. But as the engine warms up, the idling issues may eventually disappear. However, this doesn’t mean the check engine light will turn OFF. Although there are some cases the check engine light will only be present upon starting the motor, and will go away once the engine is fully warmed up.
How much does it cost to fix P0135 Fault?
If the fault is caused by shorted wiring or broken electrical connectors, the cost of fixing the problem is not much. You can expect to spend around $30 or $50 to fix a minor wiring issue. Make sure to replace the fuse in the heater circuit after fixing a short in the wiring to prevent problems later on.
But if you happen to be dealing with a bad O2 sensor, the cost of replacement will vary on the make and model of the vehicle. A typical oxygen sensor will only cost around $25 to $50 each.
Before replacing the O2 sensor, make sure the problem is not caused by issues in the wiring harness. You don’t want to end up buying a new sensor only to find out the P0135 code is caused by a wiring problem in the first place.