What Does P1135 Mean?
This code indicates a malfunction in the air/fuel ratio sensor heater circuit for Bank 1, Sensor 1 (upstream). The heater is critical for bringing the wideband A/F sensor to its operating temperature of approximately 650-700 degrees Celsius within seconds of engine start. Without proper heater function, the sensor cannot provide accurate air/fuel ratio feedback, causing open-loop operation and increased emissions during warm-up.
Common Causes
35%
Failed A/F sensor internal heater element (open circuit or high resistance)
25%
Corroded or damaged heater circuit connector or wiring
15%
Blown heater circuit fuse or faulty relay
10%
ECM heater driver circuit fault
15%
Poor chassis or engine ground affecting heater circuit
Diagnostic Steps
1
Check the A/F sensor heater fuse in the engine compartment fuse box; replace if blown and investigate for shorts.
2
Measure the A/F sensor heater resistance at the connector (disconnect sensor first); compare to spec (typically 2-8 ohms for wideband sensors).
3
Verify 12V power supply is present at the heater circuit connector with key on engine off.
4
Check the heater ground circuit for continuity and low resistance back to the ECM.
5
Monitor heater current draw with a scan tool or ammeter during cold start; it should draw 1-4 amps initially then stabilize.
6
Replace the A/F ratio sensor if the heater element is open or out of resistance specification.
Estimated Repair Cost
$150 - $450
Parts + labor, varies by vehicle and location
This code indicates a malfunction in the air/fuel ratio sensor heater circuit for Bank 1, Sensor 1 (upstream). The heater is critical for bringing the wideband A/F sensor to its operating temperature of approximately 650-700 degrees Celsius within seconds of engine start. Without proper heater funct...
The most common cause of P1135 (Air/Fuel Ratio Sensor Heater Circuit Malfunction (Bank 1 Sensor 1)) is: Failed A/F sensor internal heater element (open circuit or high resistance)
Typical repair costs for P1135 range from $150 to $450, depending on the vehicle, location, and whether you do it yourself or go to a shop.
No immediate safety hazard. However, extended open-loop operation during warm-up causes poor fuel metering and elevated emissions. Catalyst efficiency may be reduced if the sensor never reaches operating temperature.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P1135 to identify the root cause.
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Quick Info
Category
Powertrain
System
Fuel System / Emissions
Difficulty
Type
Manufacturer
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