Code
P1115
FORD
P — Powertrain
Engine Coolant Temperature (ECT) Sensor Circuit Intermittent High Voltage IAT - B Circuit High Input
Views:
UK: 43
EN: 101
RU: 60
AI status
Completed
Completed
100%
Causes
- Faulty ECT or IAT-B sensor (open or internal short)
- Damaged, corroded or loose sensor connector
- Open, shorted or intermittent wiring between sensor and PCM
- Short to battery voltage on signal circuit
- High resistance in ground or reference circuit
- Faulty PCM (less common)
Symptoms
- Malfunction Indicator Lamp (MIL) illuminated
- Incorrect coolant temperature or intake air temperature reading on scan tool
- Hard cold start, extended warm-up, or poor drivability
- Erratic temperature gauge or cooling fan operation
- Reduced fuel economy or performance due to incorrect fueling adjustments
What to check
- Read freeze frame and live data with a capable scan tool; note ECT and IAT-B behavior during cold start and warming
- Visual inspection of sensor connector and wiring for corrosion, damage, or signs of heat/repair
- Backprobe sensor signal, reference (usually 5V) and ground with ignition ON; observe voltage for stability
- Measure sensor resistance at ambient and while heated (compare to specification) after removing sensor
- Wiggle test wiring while monitoring signal for intermittent changes
- Check continuity and for shorts to battery voltage and ground between sensor connector and PCM
Signal parameters
- Typical system uses a 5 V reference, signal return and ground to PCM
- ECT/IAT are NTC thermistors: cold = higher signal voltage, warm = lower signal voltage
- Expected signal range generally 0.5–4.5 V depending on temperature (refer to vehicle-specific chart)
- Intermittent high voltage means signal rises toward reference/battery voltage or spikes intermittently
- Resistance trends: resistance decreases as temperature increases (verify with service manual values)
Diagnostic algorithm
- Retrieve freeze frame and live data; note when code set and conditions (temp, key on/run).
- Visually inspect sensor, connector and harness near sensor for corrosion, bent pins, heat damage or repairs.
- With ignition ON (engine off), backprobe signal, reference and ground. Confirm steady 5 V reference and good ground. Look for signal voltage near expected ambient value.
- Monitor signal while warming engine or exposing sensor to heat/cold (hair dryer/ice) and watch for expected change. Identify intermittent jumps to high voltage.
- Perform wiggle test on harness and connector while watching live data to reproduce intermittent behavior.
- Remove sensor and measure resistance at known temperatures (ambient and heated). Compare to OEM spec. Replace sensor if out of spec.
- Check wiring continuity and insulation between sensor connector and PCM. Check for shorts to battery (12V) or ground using a DVOM.
- Repair/replace damaged wiring or connector and retest. Clear codes and perform test drive or aging to verify.
- If wiring and sensor are good and the issue persists, follow factory PCM input circuit diagnostic procedure; consider PCM as last resort.
Likely causes
- Corroded/loose sensor connector allowing intermittent high voltage
- Sensor internal failure producing high resistance/voltage
- Wiring short to 12V (pin contact, chafing, rodent damage)
- Poor ground or high resistance in reference/ground circuit
- Intermittent PCM input circuit fault
Fault status
Status
P1115 - ECT Sensor Circuit Intermittent High Voltage / IAT-B Circuit High Input (Ford manufacturer-specific)
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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