What Does P00B5 Mean?
The radiator coolant temperature sensor is producing erratic or intermittent signal readings that fall outside expected patterns. The PCM detects rapid voltage fluctuations or signal dropouts that don't correspond to normal coolant temperature changes. The driver may notice intermittent cooling fan behavior, fluctuating temperature readings on the gauge, or the MIL illuminating and then going out sporadically.
Common Causes
35%
Loose or intermittent connection at the RCT sensor connector
25%
Chafed or intermittently grounding wiring in the sensor circuit
25%
Failing RCT sensor with intermittent internal contact
10%
Corroded PCM connector pins affecting signal integrity
5%
Electromagnetic interference from nearby ignition or charging components
Diagnostic Steps
1
Monitor the RCT sensor PID in live data while wiggling the sensor connector and harness — watch for sudden voltage spikes or dropouts that confirm an intermittent connection.
2
Inspect the sensor connector for spread or corroded terminals; apply dielectric grease and re-seat the connection.
3
Perform a wiggle test along the entire wiring run from the sensor to the PCM while monitoring the signal voltage on a DVOM or scope — isolate the fault location.
4
If no wiring fault is found, measure sensor resistance at operating temperature and compare to specs — an intermittently failing NTC thermistor may show unstable ohm readings.
5
Check for proper wire routing and separation from high-voltage ignition wires or alternator harness that could induce noise.
Estimated Repair Cost
$50 - $250
Parts + labor, varies by vehicle and location
The radiator coolant temperature sensor is producing erratic or intermittent signal readings that fall outside expected patterns. The PCM detects rapid voltage fluctuations or signal dropouts that don't correspond to normal coolant temperature changes. The driver may notice intermittent cooling fan ...
The most common cause of P00B5 (Radiator Coolant Temperature Sensor Circuit Intermittent/Erratic) is: Loose or intermittent connection at the RCT sensor connector
Typical repair costs for P00B5 range from $50 to $250, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Generally safe to continue driving. The intermittent nature means the PCM usually has valid data most of the time. However, if the cooling fans are not activating consistently, monitor engine temperature closely in stop-and-go traffic or hot weather to prevent potential overheating.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P00B5 to identify the root cause.
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Quick Info
Category
Powertrain
System
Engine Cooling System
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
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