Code
P1135
SCION
P — Powertrain
Air-fuel ratio sensor heater circuit response malfunction
AI status
Completed
Completed
100%
Causes
- Blown fuse or failed heater relay
- Open or shorted heater element inside A/F sensor
- Damaged wiring or corroded/loose connector to the sensor
- Poor or missing power or ground to the heater (battery/relay/fuse issue)
- Intermittent connection from vibration or heat damage
- ECM/PCM heater driver failure
Symptoms
- Malfunction Indicator Lamp (MIL) illuminated (check engine light)
- Possible poor cold‑start AFR control or drivability until system warms
- Reduced fuel economy or slightly unstable idle during warmup
- Failed emissions test or readiness monitor incomplete
- Diagnostic trouble code P1135 stored, possibly along with related heater codes
What to check
- Read and record freeze‑frame and live data with a scan tool; confirm P1135 and any related codes
- Visually inspect A/F sensor connector and wiring for damage, corrosion, heat melt, or exhaust contact
- Check relevant fuses and any heater relay for continuity and correct operation
- With ignition ON (engine OFF) backprobe heater power and ground circuits; verify battery voltage to heater feed when commanded
- Measure heater element resistance at the sensor (unplugged) with an ohmmeter
- Command heater ON with a scan tool (if supported) and monitor voltage/current at the connector
Signal parameters
- Heater supply voltage: near battery voltage (~12 V) to heater feed when heater is commanded ON (varies by model)
- Heater element resistance (cold): typically low ohms — commonly on the order of 1–20 Ω depending on sensor type (refer to vehicle service data for exact spec)
- Heater current when energized: typically under a few amps (varies by sensor design)
- ECM heater command: ON/OFF status available in live data (scan tool)
- Sensor temperature rise/time: ECM expects heater to reach operating behavior within defined response time; lack of expected response triggers P1135
Diagnostic algorithm
- Retrieve and record all DTCs and freeze‑frame data. Note related codes (other heater or A/F sensor codes).
- Perform a visual inspection of the A/F sensor, connector and harness for damage, corrosion, rodent chewing, or exhaust contact. Repair visible damage before further testing.
- Check fuses and relays for the heater circuit; replace any blown fuses or faulty relays and retest.
- Unplug the sensor connector. Measure heater element resistance across the heater terminals with an ohmmeter. Compare to service specification. An open circuit or out‑of‑range reading indicates a bad sensor.
- With the connector unplugged, check for battery voltage at the heater power feed terminal with ignition ON (engine OFF). If no voltage, trace back to fuse/relay/connection.
- Check for a good ground at the heater ground terminal. Repair any poor ground connections.
- If voltage and ground are present, command the heater ON using a scan tool (if supported) and measure voltage/current at the sensor connector; observe for expected current draw. If supply is present but heater draws no current (open), sensor is faulty.
- If heater is shorting (very low resistance) and blowing fuse, isolate shorted wiring or replace sensor. Perform wiggle tests along harness while monitoring for intermittent faults.
- If wiring, connectors, fuse and relay are good but heater still fails, suspect ECM heater driver fault — confirm with manufacturer procedures before replacing ECM.
- After repair or sensor replacement, clear codes and perform a drive cycle or readiness test to verify the fault does not return.
Likely causes
- Open heater element in A/F sensor (internal break)
- Shorted heater element or short to chassis/12V
- Faulty fuse or relay in heater feed circuit
- Corroded or disconnected connector at the sensor (water/soot)
- Broken/chafed wiring in harness between ECM and sensor heater
- ECM driver transistor fault (less common)
Fault status
Status
Air‑fuel ratio sensor heater circuit response malfunction — heater did not respond as expected (open/short/intermittent or poor supply/ground). Inspect heater circuit, wiring, connector, fuse/relay and sensor.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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