Code
P1135
FIAT
P — Powertrain
Piston position 3 fault | Oxygen sensor B1-S2 fault | Upstream heater resistance 1 fault
Views:
UK: 11
EN: 9
RU: 5
AI status
Completed
Completed
100%
Causes
- Heater circuit open (broken wire, connector or pin)
- Heater circuit short to ground or battery
- Failed oxygen (lambda) sensor (heater element or sensing element)
- Blown fuse or faulty relay supplying sensor heater
- Corroded/loose connector or high resistance in wiring
- Faulty Engine Control Module (ECM) or poor ground
Symptoms
- Check Engine Light (MIL) on, fault stored (P1135)
- Poor fuel economy or rough running if ECM reverts to open-loop
- Delayed warm-up emissions control
- Possible failed readiness/failed O2 sensor monitoring
- Occasional misfires or hesitation under some conditions (if ECM limits closed-loop)
What to check
- Read freeze frame and pending codes with a scanner; confirm P1135 and any related codes (heater circuit or O2 sensor codes)
- Visually inspect O2 sensor(s) and wiring harness around exhaust for damage, chafing, corrosion or heat damage
- Check for blown fuses and any related relays that feed the sensor heater circuit
- With ignition off, measure heater element resistance at the sensor connector (unplug sensor first)
- Check supply voltage to heater connector with ignition ON (usually battery voltage) and probe ground continuity
- Perform wiggle test on harness while monitoring live data/voltage to reproduce fault
Signal parameters
- Typical upstream O2 (narrowband) sensor voltage (heated): approx. 0.1–0.9 V switching when in closed-loop
- Heater supply voltage: ~11–14 V with ignition ON (depends on vehicle)
- Heater resistance (typical range): about 2–20 Ω for many heated O2 sensors (manufacturer dependent) — consult Fiat spec
- Heater current: may be 0.5–3 A depending on sensor type
- If heater circuit open: infinite resistance (OL) between heater pins; if shorted to ground: near 0 Ω to chassis
Diagnostic algorithm
- Confirm code and related codes with a scan tool; record freeze frame and live data.
- Visually inspect sensor(s), connectors and wiring for heat damage, breaks, corrosion or rodent damage. Repair any obvious damage.
- With ignition off and sensor disconnected, measure heater resistance across heater pins. Compare to Fiat spec. If open or out of range, replace sensor.
- With connector plugged, measure supply voltage to the heater feed with ignition ON—there should be battery voltage or switched voltage per Fiat spec. If no supply, inspect fuses/relays and wiring back to power source.
- Check ground/ECU driver: measure continuity from sensor ground pin to chassis ground, and check for shorts to battery. If ground/open/short present, repair wiring or connector.
- If supply and ground OK but heater draws abnormal current, replace sensor. If wiring checks OK and replacement sensor also faults, test/replace ECM or repair connector to ECM.
- Clear codes and perform road/drive cycle to confirm repair and readiness monitors set. Document results.
Likely causes
- Damaged or disconnected heater power/ground wire at Bank 1 sensor
- O2 sensor heater element has failed (internal open or high resistance)
- Connector corrosion causing intermittent continuity or high resistance
- Related fuse or relay has failed
- ECM driver for heater has malfunctioned
Fault status
Status
ECM detected abnormal oxygen sensor/heater circuit behavior on Bank 1 (open, short, high resistance or no activity). MIL set (P1135). Closed‑loop fueling may be disabled until the fault is corrected.
Repair difficulty: Medium
Diagnostic time: 0.5-2.5 hours
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