Code
P1135
LEXUS
P — Powertrain
Air/Fuel Ratio Sensor Heater Circuit Malfunction Bank 1 Sensor 1
Views:
UK: 37
EN: 74
RU: 38
AI status
Completed
Completed
100%
Causes
- Failed A/F sensor (heater element open or internally shorted)
- Open or damaged heater wiring or connector (broken wire, chafing)
- Blown fuse, faulty relay or power supply to the heater circuit
- Poor connector contact or corrosion at sensor or harness
- Short to ground or short to battery in heater circuit
- PCM driver fault or poor PCM ground
Symptoms
- Malfunction Indicator Lamp (MIL) / Check Engine light ON
- Longer warm‑up time to closed‑loop fueling; poor cold emissions
- Possible rough idle or drivability issues during cold start
- Reduced fuel economy until sensor reaches operating temperature
- Failed emissions test (excess cold‑start emissions)
What to check
- Scan for stored/active codes and note freeze frame / live data
- Visual inspection of sensor, connector and wiring for damage, corrosion or exhaust leaks
- Verify relevant fuses and relays for heater circuit are intact
- Backprobe harness at sensor to check for battery voltage on heater supply pin with ignition ON
- Monitor PCM heater command (on/off) in live data while engine is cold
- Measure heater element resistance at sensor with connector disconnected (cold)
Signal parameters
- Heater supply voltage: approximately battery voltage (~11–14 V) to heater supply pin when key ON
- Heater control: PCM typically switches the heater to ground (or supplies ground) — check live command
- Typical heater resistance: manufacturer dependent; commonly in the low ohm range (about 2–20 Ω). Consult OEM spec for exact value
- Expected heater current: up to a few amps when energized (varies by sensor)
- When functioning, heater will draw current immediately when commanded and help the sensor reach operating temp quickly (no precise temp spec without OEM data)
Diagnostic algorithm
- Confirm code P1135 with a scan tool. Record freeze frame and live data. Verify fault is current or stored.
- Perform a visual inspection of the Bank 1 Sensor 1 harness and connector. Look for corrosion, damaged insulation, heat damage or pinned/bent terminals.
- Check fuses and relays related to the oxygen/A‑F sensor heater circuit; replace if blown or faulty.
- With ignition ON (engine OFF), backprobe the heater power terminal at the sensor connector. Verify battery voltage is present on the supply side.
- Command the heater ON with a capable scan tool and observe PCM heater command in live data. While commanded, measure voltage/current at the heater supply and driver side to confirm the circuit is being driven.
- With connector disconnected and ignition OFF, measure resistance of the heater element between the heater pins on the sensor. Compare to OEM spec. An open or very high resistance indicates a failed heater.
- Check continuity from the harness connector to the PCM heater driver pin and to ground as appropriate. Look for shorts to ground or battery that would prevent proper operation.
- Perform a wiggle/strain test on harness while monitoring heater circuit to detect intermittent faults.
- If wiring and power/grounds are correct but heater resistance is out of spec, replace the A/F sensor. Clear codes and perform a test drive to confirm the code does not return.
- If the new sensor reports correctly but the code persists, suspect PCM driver fault or intermittent wiring; consult wiring diagrams and consider PCM testing/replacement as a last resort.
Likely causes
- Failed A/F sensor heater (most common)
- Open or high‑resistance heater wiring or connector at sensor
- Blown fuse / defective heater power relay or fusible link
- Corroded / loose connector at sensor harness
- Short to ground in harness or poor PCM driver
Fault status
Status
PCM detected heater circuit malfunction for Air/Fuel Ratio Sensor Bank 1 Sensor 1 (heater open, short, high resistance, or heater driver fault).
Repair difficulty: Medium
Diagnostic time: 1.0-2.5 hours
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Repair manuals
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LEXUS
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LEXUS: 2023
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ES 250
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