Code
P00B1
Generic
P — Powertrain
Radiator Coolant Temperature Sensor Circuit
Views:
UK: 17
EN: 36
RU: 24
AI status
Completed
Completed
100%
Causes
- Faulty/failed radiator coolant (ECT) sensor
- Open or shorted wiring between sensor and PCM (to ground or battery voltage)
- Corroded, loose or damaged sensor connector/terminals
- Poor or missing sensor ground or reference voltage at the connector
- Intermittent wiring damage from chafing or heat
- Faulty PCM (rare)
Symptoms
- Check Engine Light / MIL illuminated
- Incorrect coolant temperature reading on gauge or scan tool
- Hard cold/hot starting, poor idle or erratic idle speed
- Reduced fuel economy or rich/lean drivability issues
- Cooling fan may run incorrectly (on too early/late) or not run
- Possible engine overheating if cooling control is affected
What to check
- Read and record freeze-frame and live coolant temperature data with a scan tool.
- Visually inspect sensor, connector and harness for corrosion, damage, pin backs-out, or signs of overheating.
- Check coolant level and thermostat operation to rule out mechanical cooling issues affecting readings.
- With ignition ON (engine off), backprobe connector to verify reference voltage and ground presence.
- Measure sensor resistance at known coolant temperatures and compare to OEM chart, or measure sensor voltage signal while warming engine.
- Perform wiggle/strain test on wiring while monitoring live data to reproduce intermittent faults.
Signal parameters
- Sensor type: typically an NTC thermistor (resistance decreases as temp increases).
- Resistance: varies by manufacturer — expect high resistance at cold and low resistance at hot (example range across full operating temp commonly hundreds ohms to several kilo-ohms).
- Signal voltage (typical): varies by circuit design; commonly measured between ~0.1–4.5 V depending on temperature and whether circuit uses pull-up/pull-down. Consult OEM spec.
- Reference voltage (sensor supply): typically ~5 V or ignition-switched reference — must be present at connector with key ON.
- Ground: solid low-resistance ground is required at sensor connector.
Diagnostic algorithm
- Retrieve codes and live data using a scan tool; note coolant temp reading and whether value is fixed, fluctuating, or out-of-range.
- Perform visual inspection of sensor, connector and wiring harness near radiator and engine for damage, corrosion or pin issues.
- With ignition ON (engine off) backprobe connector: confirm reference voltage present and verify good ground; record voltages.
- Measure sensor resistance (remove sensor if needed) at ambient temperature and compare to OEM resistance vs temperature chart. If no chart, verify resistance changes when warmed (by hand or warm coolant).
- Check for shorts: with meter, check continuity from signal wire to ground and to battery positive to detect shorts. Repair any short or open.
- If signal and wiring check out but scan tool shows incorrect temperature, wiggle harness while observing live data to find intermittent faults.
- Replace sensor if resistance/voltage is out of specification or sensor is intermittent. Retest system and clear codes.
- If fault persists after sensor and wiring repairs, check PCM power/ground and inputs; consult manufacturer procedures before replacing PCM.
- After repair, perform road test and monitor ECT readings and cooling fan operation; clear codes and verify code does not return.
Likely causes
- Open circuit in sensor signal or ground (broken wire, connector pushed out)
- Short to ground or battery voltage in sensor harness
- Corroded/contaminated connector causing high resistance or intermittent contact
- Failed ECT sensor element
- Incorrect sensor installed or wrong resistance/characteristic for vehicle
Fault status
Status
Stored when the engine control module detects an open, short, or implausible signal from the radiator coolant temperature sensor circuit. The condition may set the MIL and cause incorrect coolant temperature readings, affecting fuel control, idle, emissions and fan operation.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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