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DTC codes / P00xx · Fuel and air metering and auxiliary emission controls / P00B3

P00B3Radiator Coolant Temperature Sensor Circuit Low

P00B3 indicates the engine control module has detected a low voltage signal from the radiator coolant temperature sensor circuit, which is used to monitor the temperature of the coolant leaving the radiator. The computer expects a voltage within a specific range and sets this code when the signal falls below the minimum threshold, often indicating a short to ground or an open circuit.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaFuel and air metering and auxiliary emission controls

Symptoms you may notice

  • Illumination of the check engine light, often with no other noticeable symptoms
  • Electric cooling fan may run continuously or not at all, depending on the failure mode
  • Temperature gauge may read abnormally low or not move from the cold position
  • Poor fuel economy or slightly rough running as the computer may enrich the mixture based on a false cold reading
  • In some vehicles, a message on the driver information center about a cooling system fault

Common causes, most likely first

  1. Faulty radiator coolant temperature sensor
  2. Damaged or corroded wiring harness or connector at the sensor
  3. Short to ground in the signal circuit between the sensor and the engine control module
  4. Open circuit in the sensor ground or reference voltage circuit
  5. Failed engine control module (rare but possible)
  6. Coolant contamination or sensor tip coated with debris causing incorrect resistance

How to diagnose and fix it

  1. Verify the code with a scan tool and check for any related pending or history codes
  2. Inspect the sensor connector and wiring for signs of corrosion, damage, or loose pins
  3. Measure the sensor resistance with a multimeter and compare to the manufacturer's temperature-resistance chart
  4. Check the signal circuit for a short to ground by disconnecting the sensor and measuring voltage at the connector
  5. Check the reference voltage and ground circuits at the sensor connector with the key on
  6. If wiring and sensor test good, perform a wiggle test on the harness while monitoring sensor data to detect intermittent faults
  7. Replace the radiator coolant temperature sensor if it fails resistance or voltage tests, then clear codes and verify the repair

Radiator sensor faults that mimic other codes

  • A low voltage signal can be caused by a short to ground anywhere along the signal wire, not just at the sensor, so a thorough harness inspection is essential before replacing parts.
  • The radiator coolant temperature sensor is often confused with the engine coolant temperature sensor; P00B3 specifically refers to the radiator outlet sensor, which monitors coolant after it has passed through the radiator.
  • In some vehicles, a failed radiator coolant temperature sensor can cause the cooling fan to run constantly, leading to overcooling and a false low-temperature reading that affects fuel trim and emissions.
  • A poor ground connection at the sensor or at the engine block can produce the same low voltage code, so checking ground integrity is a critical step that is frequently overlooked.
  • This code can be set by a momentary glitch in the signal, so intermittent faults may not appear during a static test; a road test with live data monitoring is often needed to reproduce the condition.

Can I keep driving with P00B3?

It is generally safe to drive with this code as long as the engine temperature gauge does not show overheating and the cooling fan operates normally. Avoid sustained heavy loads or towing until the fault is repaired, as the computer may not command the fan correctly, potentially leading to overheating in extreme conditions.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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