Code
P1135
ALFA ROMEO
P — Powertrain
Piston position 3 fault | Oxygen sensor B1-S2 fault | Upstream heater resistance 1 fault
AI status
Completed
Completed
100%
Causes
- Failed piston position (cylinder 3) position sensor or wiring
- Failed oxygen sensor (Bank 1, Sensor 2) or its heater element
- Open or short in heater circuit (power or ground)
- Blown fuse or faulty relay for O2 heater circuit
- Corroded/loose connectors or damaged wiring harness
- ECM/PCM driver fault or internal control module error
Symptoms
- Check Engine MIL (CEL) illuminated
- Poor idle, rough running or misfire—may be localized to cylinder 3
- Hard starting or extended crank time
- Reduced fuel economy and increased emissions
- Failed emissions test
- Possible lack of power or hesitation on acceleration
What to check
- Read freeze frame and full DTC list with a capable scan tool to confirm related codes
- Visual inspection of wiring and connectors for Bank 1 Sensor 2 and cylinder 3 position sensor
- Check fuses and relays associated with O2 heater circuit
- Backprobe O2 sensor heater power and ground with ignition ON; verify supply voltage and switch/ground control from ECM
- Measure heater element resistance (unplug sensor) and compare to OEM spec
- Monitor O2 sensor signal voltage (0.1–0.9 V) and switching when engine is warm and in closed loop
Signal parameters
- O2 sensor (Bank 1 Sensor 2) signal voltage: ~0.1 V (lean) to ~0.9 V (rich) when functioning; downstream sensor may be steadier than upstream
- O2 sensor heater resistance: typically a few ohms up to ~20 Ω (check OEM spec)
- Heater supply voltage: battery voltage (approx. 12 V) at fuse/relay when ignition ON
- Heater circuit current draw: commonly 0.5–2 A (varies by sensor)
- Piston/position sensor (cylinder 3) waveform: square or sinusoidal pulses referenced to engine speed, 0–5 V (or 0–12 V depending on sensor type) — must match cam/crank timing
- Scan tool live data: downstream O2 should show less switching than upstream; position sensor RPM/sync must be stable
Diagnostic algorithm
- Connect a scanner, record freeze frame, pending codes and any related DTCs (O2, cam/crank, misfires).
- Inspect connectors and wiring for Bank 1 Sensor 2 and cylinder 3 position sensor. Repair any corrosion, bent pins, or damaged insulation.
- Check fuses/relays for the O2 heater circuit. Replace if blown and test if it recurs.
- With sensor unplugged, measure O2 heater resistance and compare to spec. If open or out-of-spec, replace the sensor.
- With ignition ON, verify battery voltage at heater power feed and verify ECM provides ground/control to heater when conditions require (use backprobe or wiring diagram).
- Monitor O2 sensor signal (and downstream behavior) while engine at operating temperature. Verify expected voltage range and switching behavior for that sensor location.
- Probe piston/position sensor for cylinder 3 signal with oscilloscope or scope-capable scan tool. Confirm waveform, amplitude and timing relative to crank/cam sensors.
- If position signal is missing/intermittent, trace wiring back to ECU and check for short/open; swap known-good sensor if available to confirm.
- If wiring and sensors check good, test ECM outputs and inputs or consult manufacturer service procedures for ECM testing/reprogramming.
- If position disagreement persists, perform mechanical checks: compression/leakdown test, inspect timing belt/chain and cam/crank reluctor rings for damage or movement.
- After repairs, clear codes and perform drive cycle to confirm the fault does not return and related readiness monitors complete.
Likely causes
- O2 sensor heater element burned out or high resistance
- Disconnected or corroded O2 sensor connector (Bank 1 Sensor 2)
- Open circuit or short to voltage/ground in heater wiring
- Piston/cam/crank position sensor for cylinder 3 faulty or intermittent
- Damaged tone wheel, reluctor, or sensor mounting causing incorrect piston/position signal
- Bad ground or low battery/charging voltage causing heater not to build up
Fault status
Status
P1135 — Fault detected in cylinder 3 piston/position sensing and/or Bank 1 Sensor 2 oxygen sensor heater/resistance. Possible sensor, wiring, fuse/relay, ECM driver or mechanical timing issue. Further diagnosis required.
Repair difficulty: Medium
Diagnostic time: 1.5-4 hours
Repair manuals
Manual library for ALFA ROMEO
89
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