Fix P0135: Mechanic’s solutions that WORKED

P0135: O2 sensor heater circuit malfunction (bank 1, sensor 1) suggests a problem with the heater element on one of your oxygen sensors. It is usually caused by a faulty sensor or damage to the wiring for the O2 sensor.

P0135 quick overview

Meaning	O2 sensor heater circuit malfunction (bank 1, sensor 1).
Is it serious?	It can affect engine performance and emissions but may not necessarily lead to immediate breakdown.
Possible causes	– Faulty O2 sensor heater circuit. – Wiring issues in the O2 sensor heater circuit. – Failed O2 sensor.
How to diagnose?	Check Wiring: Inspect the wiring connected to the O2 sensor for any visible damage or disconnection. Test O2 Sensor Heater Circuit: Use a multimeter to check the resistance in the O2 sensor heater circuit. Inspect O2 Sensor: Visually inspect the O2 sensor for any signs of damage or wear. Replace O2 Sensor: If the O2 sensor is faulty, consider replacing it. Reset Codes: After addressing the issue, clear the error codes and monitor the system for any recurrence.
What is a Heater for O2 sensor?	Warms up O2 sensor for quick operation

How to fix p0135 – learn from mechanics

I looked into P0135 service cases at iatn.com website where in the private forums the mechanics seek advice from other mechanics. I looked up a bunch of cases to help you decide how to fix your issue and see what would a real mechanic do to solve it.

Case #1: Chrysler

Vehicle Information:
1997 Chrysler Sebring JX
Engine: 2.5L
Mileage: 73,978 miles

Issue + Repair History:

• Initial issue: MIL Lamp on with code P0135 for O2 sensor heater failure.
• First repair: Replaced upstream O2 sensor.
• Second repair: Replaced ASD relay.

Suggestions from the Community:

• Check if there are two upstream O2 sensors for each bank.
• Test the battery to ensure it’s not weak, as a weak battery can trigger the code.
• Investigate the O2 heater ground circuit for potential issues.
• Check O2 sensor grounds and sensor grounds.
• Consider the possibility of the PCM running the O2 heater test after engine shutdown under specific conditions.

Final Fix:
Discovered that the upstream O2 heater ground wire was cut behind the plenum. The issue was resolved by repairing the open O2 heater ground wire.

Case #2: Ford

Vehicle Information:
2001 Ford Ranger Edge
Engine: 4.0L
Mileage: 59,000 km

Issue + Repair History:

• MIL Lamp on every couple of days with code P0135 (B1S2 heater failure).
• First repair: Replaced downstream O2 sensor.
• Second repair: Checked circuit with no issues found.

Suggestions from the Community:

• Check the resistance of the heater circuit in the O2 sensor, focusing on the downstream O2 (B1S2).
• Verify battery voltage on the heater circuit with the key on and check ground circuit resistance with the key off.
• Wire a headlight into the heater circuit to check for voltage drop.
• Consider using a Motorcraft O2 sensor, as aftermarket and universal sensors may cause heater codes.
• Verify if the code is for B1S1 instead of B1S2.

Final Fix:
The scan tool initially misread the code as a downstream sensor problem when it was actually B1S1. Discovered two wires chafed on the upstream sensor, almost breaking off. The issue was fixed by repairing the chafed wires on the upstream sensor (B1S1).

Case #3: Toyota

Vehicle Information:
1996 Toyota Avalon XL
Engine: 3.0L

Issue + Repair History:

• MIL Lamp on with code P0135 (O2 sensor heater circuit malfunction, Bank 1 Sensor 1).
• Replaced front manifold upper sensor and catalytic converter.
• The coolant sensor light persisted after 20 miles of driving.

Suggestions from the Community:

• Clarify if the check engine light or coolant light is coming on.
• Ensure if the P0135 code is still present.
• Emphasize that Bank 1 Sensor 1 is by the firewall, not the front one.
• Suggest checking for coolant leaks if the coolant sensor light is on.
• Confirm the correct location of Bank 1 Sensor 1 for future reference.

Final Fix:
The initial mistake involved installing the O2 sensor in the wrong location (replaced Bank 1 Sensor 2 instead of Bank 1 Sensor 1). The issue was resolved by switching the sensors and replacing Bank 1 Sensor 1 by the firewall. After the correction, the car ran well.

Case #4: Ford

Vehicle Information:
2003 Ford F-150 Lariat
Engine: 5.4L

Issue + Repair History:

• Check engine light came on with codes P0133 and P0135 for oxygen sensor issues.
• Replaced oxygen sensor and test drove the vehicle.
• A new code P1131 appeared, indicating a Lean Bank 1 condition.
• Conducted a smoke test and changed the fuel filter.
• No leaks were found at the intake.
• Cleaned the Mass Air Flow (MAF) sensor and reset fuel trims.

Suggestions from the Community:

• Check for faulty or plugged injectors.
• Inspect and clean the air filter and MAF sensor.
• If equipped with a K&N filter, remove it and clean the MAF.
• Look for leaks in the PCV tubing, especially the rubber elbow connecting to the plenum.
• Check the PCV harness for collapse or pinholes.
• Examine the PCV hose for possible suction, causing a lean condition.
• Consider the possibility of a bad PCM (Powertrain Control Module).

Final Fix:
The MAF sensor was cleaned, and fuel trims were reset. The readings returned to normal, and no further codes reappeared.

Case #5: Honda

Vehicle Information:
2002 Honda Accord SE
Engine: 2.3L

Issue + Repair History:

• Initial concern: Hard 1-2 shift and D4 lamp flashing.
• Replaced ECM with a used unit due to P1739 (3rd clutch pressure switch fault).
• After ECM replacement, the vehicle now had hard shifts into all gears, missed shifts while driving, and appeared to go blank before catching the next gear.
• Attempted idle relearn, but P0135 (O2 sensor heater circuit malfunction) interrupted the process.
• Suspected transmission issue requiring a rebuild.

Suggestions from the Community:

• Resolve P0135 (O2 sensor heater circuit malfunction) before attempting adaptive relearn.
• Check fluid condition for signs of foreign material and solenoid issues.
• Address the 3rd pressure switch issue, which is common and might cause the D4 flashing.
• Consider checking for bearing noise and potential differential bearing failures.
• Verify fluid level, quality, and test line pressure; check for solenoid clogs or failures.
• Ensure wire harnesses on solenoids are correctly connected to prevent D4 flashing.

Final Fix:
The O2 sensor was replaced to resolve the P0135 code. An adaptive relearn was performed, but the shift issues persisted. A transmission service was conducted, and the ECM was replaced with the old one, but the problem remained.