Powertrain (Engine & Gearbox)Standard EOBD

P00B1 - Radiator Coolant Temperature Sensor 2 Circuit High

Q: What are the symptoms of fault code P00B1?

• Check engine light (MIL) illuminated • Cooling fans running at high speed constantly (failsafe mode) • Incorrect or erratic temperature readings via scan tool • Failed emissions test due to stored code

Q: What causes fault code P00B1?

• Most likely: Faulty Radiator Coolant Temperature Sensor (ECT 2) with internal open circuit • Likely: Connector issues or corrosion at the sensor pins • Possible: Wiring harness break in signal or ground return line • Rare: Faulty Engine Control Unit (ECU)

Q: How do you fix fault code P00B1?

STEP 1: Inspect the ECT 2 sensor connector (usually lower radiator hose) for corrosion or backed-out pins. Clean if necessary. STEP 2: Measure circuit voltage. With ignition ON and sensor disconnected, you should see a 5V reference. If 5V is present, the wiring to the ECU is likely intact. STEP 3: Check sensor resistance (Ohms). A typical NTC sensor at 20°C/68°F should be around 2000-3000 Ohms. Infinite resistance (OL) indicates a faulty sensor. STEP 4: Monitor 'Live Data' on a scan tool. If it reads -40°, the circuit is open. Jumper the connector pins (signal to ground); if the reading jumps to +120°C/max, the sensor is defective. STEP 5: Replace the ECT 2 sensor if measurements are out of spec. Clear codes and road test.

Last updated:1 February 2026

Related:ECT Sensor 2, Kylarslang, ECU (Engine Control Unit), Kabelstam, Thermostat

System

Powertrain (Engine & Gearbox)

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Technical Description

P00B1 is triggered when the Engine Control Unit (ECU) detects a voltage signal from the Radiator Coolant Temperature Sensor 2 (ECT 2) that is higher than the calibrated threshold (typically above 4.8V-4.9V). This sensor is usually located at the radiator outlet or lower radiator hose. The ECU utilizes ECT 2 to monitor thermostat efficiency and radiator performance. A 'Circuit High' condition typically signifies an open circuit (break in wiring) or a disconnected sensor, leading to infinite resistance and maximum signal voltage.

Possible Causes

Faulty Radiator Coolant Temperature Sensor (ECT 2) with internal open circuit

Connector issues or corrosion at the sensor pins

Wiring harness break in signal or ground return line

Faulty Engine Control Unit (ECU)

Symptoms

Check engine light (MIL) illuminated

Cooling fans running at high speed constantly (failsafe mode)

Incorrect or erratic temperature readings via scan tool

Failed emissions test due to stored code

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P00B1 - Radiator Coolant Temperature Sensor 2 Circuit High

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P00B1 - Radiator Coolant Temperature Sensor 2 Circuit High

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