Oxygen sensors play a huge role in fuel efficiency and overall vehicle performance. Mounted downstream of your engine, these sensors read the air-fuel ratio of your exhaust gases. Based on this information, your onboard computer adjusts fuel accordingly. Over time, these oxygen sensors may foul or fail altogether, which can trigger trouble codes like P0135.
The sole purpose of these sensors is to provide real-time data back to your onboard computer. This gives your vehicle the information it needs to produce power efficiently while emitting the least amount of air pollution. Based on your exhaust gases, your computer will adjust fuel trims to obtain maximum efficiency.
Should the oxygen sensor read too little oxygen in the exhaust, this tells the computer that the engine is running too rich. This too rich condition means that there is too much fuel being delivered. Your onboard computer will then attempt to dial back the fuel to help reach efficient levels.
When your 02 sensors fail or run foul, chances are you will have more than just one stored MIL trouble code. These OBDII codes help you understand why your vehicle is not running properly, or why your gas mileage is so poor. The good news is, the steps to testing and fixing P0135 issues is not difficult at all, so let’s begin.
What does code P0135 mean?
One of many oxygen sensor related trouble codes, the P0135 translates to Oxygen Sensor Heater Circuit Malfunction. The specific location of the failed 02 sensor, in this case, is Bank 1, Sensor 1. When your OBDII scan tool reports a P0135 or related trouble code, this means that there’s a problem with your oxygen sensor.
The P0135 trouble code is turned on when your PCM or Powertrain Control Module sees that the voltage is too low. In most modern vehicles, this means that the 02 sensors are reporting a voltage lower than 400mV for an extended duration of time.
Related OBDII Codes
- P0136 – O2 Sensor Circuit
- P0137 – O2 Sensor Circuit Low Voltage
- P0138 – O2 Sensor Circuit High Voltage
- P0139 – O2 Sensor Circuit Slow Response
- P0140 – O2 Sensor Circuit no Activity Detected
- P0141 – O2 Sensor Heater Circuit
- P0142 – O2 Sensor Circuit
- P0143 – O2 Sensor Circuit Low Voltage
- P0144 – O2 Sensor Circuit High Voltage
- P0145 – O2 Sensor Circuit Slow Response
- P0146 – O2 Sensor Circuit no Activity Detected
- P0147 – O2 Sensor Heater Circuit
How to Test your Oxygen Sensor
Modern 02 sensors are comprised of 4 wires, 2 of which are typically heater wires or voltage. Along with a ground wire, the last wire is the oxygen sensor signal wire, which relays information back to your computer.
Verify the engine code malfunction – Use your scan tool to get the codes from your stored MIL status. Look up the code in question to determine the exact nature of your check engine light.
Inspect vehicle – Once you have the correct code, conduct an overall vehicle inspection. You are checking for loose connections or broken and/or frayed wiring from your oxygen sensor to your ECU. Make sure to jiggle the harness in the event that wiring inside the housings have not worked themselves loose.
Check oxygen sensor heater wires – Obtain the wiring for your vehicle, and using a multimeter test for 12 volts at both heater wires. These wires provide the voltage for proper 02 sensor operation. Be sure to test the voltage from your vehicle harness, and back probe these wires with the oxygen sensor connected.
Check grounds – Now that you have checked for voltage at the harness, you’ll need to confirm a proper ground. Without this ground signal intact, there’s little chance of your 02 sensor functioning properly.
Confirm signal to ECU – The last wire is the signal wire to your PCM or Powertrain Control Module. Check for continuity between your oxygen sensor harness and the onboard computer. If there are no breaks, back pin the oxygen sensor signal wire to determine what your 02 sensor is seeing.
This signal should oscillate between 100mV and 900 mV within a 30-50 millisecond window at idle. If the sensor does not perform in this manner, emissions tests will fail the sensor and your vehicle.
Need a guide to fix P0135 check engine light issues? Here are a few below that you can use to correct any 02 sensor problems you may have.
- How To Test a Ford Taurus Oxygen Sensor
- How To Test a Honda Civic Oxygen Sensor
- How To Test a Chevy Impala Oxygen Sensor
- How To Test a Ford Mustang Oxygen Sensor
- How To Test a Chevy Tahoe Oxygen Sensor
- How To Replace a Ford Flex Oxygen Sensor
- How To Replace a Ford Fusion Oxygen Sensor
- How To Test a Chevy Silverado Oxygen Sensor
Symptoms of P0135
- Rough Idle
- Sluggish Performance
- Poor Gas Mileage
- Engine will not start
- Black smoke or soot from tailpipe
Common P0135 Issues
- Improper fuel pressure
- Leaking fuel injector
- Failed Oxygen Sensor
- Fouled Oxygen Sensor
- Intake leaks
- Bad Engine Coolant Temperature sensor
- Damaged engine harness
- Failed Powertrain Control Module
There are some cases in which the oxygen sensor will read above 1 volt or negative voltage. This is a case of an internally failed 02 sensor that must be replaced. Contamination or an excessively rich running engine can also contribute to this issue. Make sure to check for physical damage to your 02 sensor, and replace it accordingly.
