P00B2

Radiator Coolant Temperature Sensor Circuit Range/Performance

P00B2 is a generic OBD-II powertrain diagnostic trouble code: Radiator Coolant Temperature Sensor Circuit Range/Performance. It is logged by the engine control unit when the coolant monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.

Code
P00B2
Group
Powertrain
System
Coolant
Severity
Warning (MIL on)
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What P00B2 means

Code P00B2 is stored when the engine control module (ECM) detects that the radiator coolant temperature sensor (RCTS) is operating outside its expected performance range — meaning the sensor signal is present and within electrical limits but the temperature value it reports is implausible or inconsistent with other engine data. Common rationality checks include comparing the RCTS reading against the engine ECT sensor at start-up (both should be near ambient when cold-soaked), checking that the radiator temperature falls appropriately once the thermostat opens, and verifying that the temperature tracks linearly with known heat exchanger behaviour. A sensor that reads stuck at a fixed value, drifts slowly, or stays unreasonably close to engine-out temperature when the radiator should be cooler will trigger P00B2. Because the fault is a performance issue rather than a hard electrical failure, it is often caused by a degraded sensor, a stuck-open or stuck-closed thermostat affecting the expected temperature differential, or by sludge or scale coating the sensor tip. The ECM may limit cooling fan control authority, affecting engine thermal management, until the fault is resolved.

Common causes

Most-frequently reported root causes when P00B2 is logged.

  • 1
    Degraded radiator coolant temperature sensor with a shifted resistance curve, reading plausible voltages but incorrect temperatures
  • 2
    Stuck-open thermostat causing radiator temperature to track engine-out temperature too closely, failing the expected differential check
  • 3
    Sludge, scale, or air pocket around the sensor tip preventing accurate coolant contact and causing a sluggish or fixed reading
  • 4
    Coolant mixing issue (low coolant concentration) altering thermal properties and defeating rationality thresholds
  • 5
    Intermittent wiring fault causing the sensor to occasionally drop to a fixed value that the ECM flags as implausible
  • 6
    Faulty engine ECT sensor providing incorrect engine-side temperature data, causing the cross-check with RCTS to fail
  • 7
    ECM calibration issue or software fault interpreting a valid but edge-case sensor reading as out of range (check for TSBs)

Symptoms drivers notice

Check Engine Light (MIL) illuminated
Cooling fans operating at incorrect times — either running too early, too late, or continuously
Temperature gauge behaving abnormally, such as climbing slowly to operating temperature or staying lower than normal
Reduced fuel economy and slightly rough idle as the ECM adjusts fuelling strategy based on incorrect coolant temperature data
Engine running richer than normal during warm-up because the ECM believes the engine is colder than it is
Possible companion codes for thermostat performance (P0128) or cooling fan faults if the ECM detects a related system anomaly

How to diagnose P00B2

A typical diagnostic flow when this code is present.

  1. 1
    Retrieve all stored codes; pay particular attention to thermostat codes (P0128) or companion CTS codes that may reveal the root cause
  2. 2
    With a scan tool, compare the live RCTS and ECT sensor readings at cold start — both should read within a few degrees of ambient; a large offset confirms a faulty sensor
  3. 3
    After a full warm-up cycle, verify the RCTS reading drops below the ECT reading once the thermostat opens; if RCTS tracks ECT closely, suspect a stuck-open thermostat
  4. 4
    Inspect the sensor tip for scale, rust, or sludge that could insulate it from the coolant; clean or replace as needed
  5. 5
    Test sensor resistance at a known temperature and compare to the manufacturer's specification curve; a shifted curve confirms sensor degradation
  6. 6
    Check coolant condition and concentration; diluted or degraded coolant can alter thermal properties enough to affect rationality thresholds
  7. 7
    After repairs, clear codes and perform a complete warm-up drive cycle with scan-tool data logging to confirm RCTS and ECT readings are plausible and diverge correctly after thermostat opening

Related powertrain codes

Frequently asked questions

What does 'range/performance' mean compared to a plain circuit fault?

A plain circuit fault (P00B1) means the electrical signal is outside acceptable voltage limits — the wire is open or shorted. A range/performance fault (P00B2) means the voltage is within electrical limits but the temperature value reported is implausible when compared to other engine data. The sensor is electrically alive but functionally wrong.

Can a stuck-open thermostat cause P00B2?

Yes. If the thermostat is stuck open, hot coolant flows through the radiator continuously and the radiator temperature stays close to engine-out temperature. The ECM expects the radiator to be cooler than the engine once the thermostat opens; when it isn't, it flags the RCTS signal as implausible.

Is it safe to continue driving with P00B2?

Short trips are generally tolerable, but the cooling fans may operate incorrectly, increasing overheating risk in heavy traffic or hot weather. Monitor the temperature gauge closely and arrange diagnosis promptly.

Will flushing the cooling system fix P00B2?

If the fault is caused by scale or sludge on the sensor tip, or by degraded coolant affecting thermal properties, a cooling system flush can help. However, if the sensor itself has a shifted resistance curve or the thermostat is stuck, a flush alone will not resolve the code.

Disabling P00B2 in software

RaceTune can permanently disable P00B2 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.

Permanent
The monitor is disabled in the ECU itself — not just cleared. It cannot return.
Tailored to your file
Each patch is matched to your specific software version — never a one-size-fits-all file.
Reversible
The original file is always preserved. Reflash the stock to return the ECU to factory state.

Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.

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