What causes fault code P00B5?

• Most likely: Faulty Radiator Coolant Temperature (ECT) sensor 2 • Likely: Corrosion or poor connection in the sensor connector • Possible: Stuck or malfunctioning thermostat causing irrational temperature deltas • Rare: Wiring harness issues (short to ground/voltage) or air pockets in the cooling system

How do you fix fault code P00B5?

STEP 1: Check coolant levels and inspect for leaks. Perform a visual inspection of the ECT 2 sensor connector for corrosion or backed-out pins. STEP 2: Use a scan tool to monitor Live Data. Compare ECT 1 and ECT 2 on a cold engine; they should be nearly identical. Under warm-up, ECT 2 should follow ECT 1 but with a predictable delay. STEP 3: Test the sensor resistance (Ohms). Typical NTC values: ~2500 Ohms at 20°C (68°F). Verify 5V reference voltage and ground circuit integrity. STEP 4: If wiring is intact but the sensor response remains erratic, replace ECT sensor 2. Bleed the cooling system to ensure no air pockets remain.

Powertrain (Engine & Gearbox)Standard EOBD

P00B5 - Radiator Coolant Temperature Sensor 2 Circuit Intermittent/Erratic

Q: What are the symptoms of fault code P00B5?

• Check Engine Light (MIL) illuminated • Engine cooling fans running at high speed constantly • Inaccurate readings on the temperature gauge • Vehicle may enter Limp Home mode • Possible erratic idle or slightly increased fuel consumption

Last updated:1 February 2026

Related:ECT Sensor 2, Thermostat, Engine Control Module (ECM), Cooling Fan Relay, Wiring Harness

System

Powertrain (Engine & Gearbox)

Related Fault Codes

P0000

No Diagnostic Trouble Codes (DTC) Present

P0001

Fuel Volume Regulator Control Circuit / Open

P0002

Fuel Volume Regulator Control Circuit Range/Performance

P0003

Fuel Volume Regulator Control Circuit Low

Technical Description

P00B5 is set when the Engine Control Module (ECM) detects that the signal from Engine Coolant Temperature (ECT) sensor 2 is erratic or reacting too slowly. ECT 2 is typically located at the radiator outlet to monitor radiator efficiency. The ECM compares the readings from ECT 2 with ECT 1 and other sensors like Intake Air Temperature (IAT). If the voltage signal from ECT 2 does not change within a calibrated timeframe or shows irrational jumps, the rationality check fails. This can disrupt electric fan control and active grille shutter systems.

Possible Causes

Faulty Radiator Coolant Temperature (ECT) sensor 2

Corrosion or poor connection in the sensor connector

Stuck or malfunctioning thermostat causing irrational temperature deltas

Wiring harness issues (short to ground/voltage) or air pockets in the cooling system

Symptoms

Check Engine Light (MIL) illuminated

Engine cooling fans running at high speed constantly

Inaccurate readings on the temperature gauge

Vehicle may enter Limp Home mode

Possible erratic idle or slightly increased fuel consumption

Do you also have
other fault codes?

See how P00B5 connects with your other fault codes. Our advanced analysis tool identifies causal relationships and root causes directly.

Analyze multiple codes

P00B5 - Radiator Coolant Temperature Sensor 2 Circuit Intermittent/Erratic

Related Fault Codes

Technical Description

Possible Causes

Symptoms

Recommended Solution

Workflow

Mechanic's Tip

Do you also have
other fault codes?

P00B5 - Radiator Coolant Temperature Sensor 2 Circuit Intermittent/Erratic

Related Fault Codes

Technical Description

Possible Causes

Symptoms

Recommended Solution

Workflow

Mechanic's Tip

Do you also have other fault codes?

Do you also have
other fault codes?