P00B6

Code

Generic P — Powertrain

Radiator Coolant Temperature/Engine Coolant Temperature Correlation

Brand: Generic

Type: P — Powertrain

Views: UK: 25 EN: 44 RU: 31

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Page language: EN

Causes

Faulty radiator coolant temperature sensor
Faulty engine coolant temperature (ECT) sensor
Wiring harness damage, opens, shorts, or high resistance between sensors and ECM
Poor or intermittent connector contact or corrosion
Low or contaminated coolant, air pockets in cooling system, or incorrect coolant flow
Stuck open/closed thermostat or restricted coolant flow

Symptoms

MIL/Check Engine Light illumination with P00B6 stored
Temperature gauge behaves erratically or shows incorrect temperature
Cooling fans cycling incorrectly or running continuously
Long engine warm-up time or heater not reaching normal temperature
Poor idle, rough running or reduced fuel economy if ECM uses temp data for fueling
Issues with emissions systems or regeneration (diesel) due to incorrect temp data

What to check

Read freeze frame data and live sensor values with a scan tool; note temperatures from radiator sensor and ECT sensor at cold idle, warm idle and during driving
Visually inspect coolant level, radiator cap, hoses and thermostat condition
Inspect connectors and wiring for corrosion, loose pins, damaged insulation or evidence of heat/chemical damage
Backprobe sensor signals and measure voltages and grounds with key on and engine running
Measure sensor resistances (or voltage output) and compare to manufacturer specifications or known-good sensor behavior while heating/cooling
Wiggle wiring and connector while observing live data for intermittent faults

Signal parameters

Typical coolant temperature sensor outputs: 0.2–4.8 V signal range (varies by vehicle, lower voltage = higher temp for many NTC sensors)
Thermistor resistance behavior: resistance decreases as temperature rises (typical order of magnitude only — consult OEM chart for exact values)
Expected correlation: radiator and engine coolant sensor temperatures should track closely once system is at steady state (difference usually small; often
Scan-tool parameters: both sensor temps should rise/ fall together during warm-up and under load; abrupt divergences indicate circuit/sensor fault
Watch for inconsistent response times: one sensor lagging significantly behind the other suggests flow/thermostat or sensor placement issue

Diagnostic algorithm

Record freeze-frame and live data from both coolant temperature sensors with a scan tool. Note operating conditions when the fault set.
Visually inspect coolant level, radiator cap, hoses and thermostat. Top up and remove air if coolant is low or aerated.
Inspect connectors and wiring at both sensors and at the ECM for corrosion, loose pins, damaged insulation or evidence of shorting. Repair any issues found.
With engine cold then warming to operating temp, monitor both sensor readings. Check that they rise at similar rates; if one lags or reads implausibly high/low, suspect that sensor or its circuit.
Measure sensor resistance (or output voltage) against temperature. Heat/cool the sensor slowly (infrared heat source or warm water) and verify change matches expected thermistor behavior. Replace sensor if out of spec.
Perform a wiggle/stress test on wiring while observing live data to catch intermittent opens/shorts. Repair or replace damaged wiring/harness as required.
If wiring and sensors test good, verify thermostat and coolant flow (bypass radiator to check behavior if safe). Replace thermostat or flush system if flow issues or air pockets are present.
If problem persists after sensors, wiring and cooling system checks, consider ECM software or internal fault; verify correct calibration and consider reflash or replacement per manufacturer guidance.
Clear the DTC and road-test through the conditions where it occurred to confirm repair. Recheck for reappearance and re-scan for related codes.

Likely causes

One coolant temperature sensor failed or drifting
Connector corrosion or pin damage at one sensor
Broken, chafed or shorted sensor signal/ground/return wire
Air trapped in the cooling system causing sensor locations to read differently
Thermostat stuck or partially blocked radiator flow producing different sensor temperatures
Intermittent wiring fault causing occasional mismatch