The OBD2 code P1135 is a diagnostic trouble code (DTC) that indicates a problem with the heater circuit in your vehicle’s Air Fuel (A/F) sensor. This code, along with potentially P1155, can be confusing, but understanding the function of the A/F sensor heater and how to diagnose issues can save you time and money. As a mechanic at obd-de.com, I’ll break down what P1135 means, how to diagnose it effectively, and what steps you can take to resolve it.
Decoding P1135 and P1155: Heater Circuit Malfunctions
Codes P1135 and P1155 directly point to issues within the heater element of your A/F sensors. These codes often appear immediately upon engine startup, particularly if there’s an open or broken heater element within the sensor. The engine control module (ECM) monitors the heater circuit, and if it detects an amperage draw outside the normal range—specifically more than 8 amps or less than 0.25 amps—it will set either P1135 or P1155. The specific code depends on which bank the affected sensor is located.
Initially, encountering P1135 might lead you to suspect a faulty front A/F sensor. However, a common diagnostic step of swapping front and rear sensors can sometimes lead to the code changing from P1135 to P1155. This crucial shift isn’t a sign of fixing the problem, but rather a key indicator: it isolates the issue to the A/F sensor itself, specifically the heater element. The codes “follow” the sensor, demonstrating that the fault is within the sensor unit, not necessarily the vehicle’s wiring harness.
Diagnosing a Faulty A/F Sensor Heater Element
If, after clearing the codes, P1135 or P1155 reappears instantly, this strongly suggests an open circuit in the heater element. If the code returns after a delay, it may indicate a heater element that is failing but not completely open. The sensor swap method, as mentioned, is a practical first step in confirming this.
For a definitive diagnosis, you can directly test the resistance of the A/F sensor heater element. This requires an Ohm meter and access to the sensor terminals.
Here’s how to test the heater element resistance:
- Disconnect the Sensor: Unplug the connector from the A/F sensor you suspect is faulty.
- Locate Heater Terminals: Identify the terminals for the heater element. These are typically the black wires on Denso OEM A/F sensors. Refer to your vehicle’s service manual for specific terminal identification if needed.
- Measure Resistance: Using your Ohm meter, measure the resistance across these terminals on the sensor side (not the harness side).
- Interpret Readings:
- Normal Resistance: At approximately 68°F (20°C), the resistance should be around 1.4 ohms. At 78°F (25.5°C), it should be about 1.1 ohms. A general acceptable range is between 0.8 and 1.4 ohms, depending on ambient temperature.
- High Resistance: Readings significantly higher than 1.4 ohms may indicate a failing heater element drawing insufficient current.
- Infinite Resistance (Open Circuit): This reading confirms an open or broken heater element, which is a definitive fault.
An oxygen sensor connector, similar to an A/F sensor connector, highlighting the terminals that can be tested for resistance to diagnose heater circuit issues.
Measurements outside the acceptable range indicate a problem with the A/F sensor’s heater element, likely necessitating sensor replacement.
OEM vs. Aftermarket A/F Sensors: A Word of Caution
When replacing A/F sensors, especially for heater circuit related codes like P1135, opting for Denso OEM (Original Equipment Manufacturer) sensors is generally recommended. While aftermarket “splice-in” sensors might seem like a cost-effective alternative, numerous reports and experiences suggest they can be problematic. Issues with reliability and compatibility can arise, sometimes leading to recurring codes or improper sensor function. Investing in the correct OEM sensor often ensures proper function, longevity, and avoids potential complications down the road.
Conclusion: Addressing OBD2 Code P1135
OBD2 code P1135 effectively pinpoints a problem within the heater circuit of your Air Fuel sensor. By understanding the diagnostic steps, including sensor swapping and resistance testing, you can accurately determine if the A/F sensor heater element is faulty. Remember, accurate diagnosis is key to effective repair. When replacement is needed, considering OEM parts can contribute to a more reliable and lasting solution for your vehicle.
