P05C6: Engine Coolant Pressure Sensor Circuit Intermittent/Erratic

An engine coolant pressure sensor (5 V reference, ratiometric signal) measures pressure in the cooling circuit; in a sealed circuit pressure rises with temperature, so deviations reveal leaks or a loose cap – described in Navistar and GE patents for commercial and rail engines. No manufacturer document available to us uses P05C2–P05C6 for passenger cars; CARB requires input components to be checked for circuit faults, range and plausibility. P05C6 means the signal jumps faster than physically possible or drops out briefly – usually a loose contact or chafed wire; with digital sensors, corrupted messages.

Symptoms

• Check engine light or warning (depending on the maker)
• Coolant pressure or leak warning unavailable
• Usually no change in driving

Most likely causes

• Loose contact or connector corrosion
• Chafed wire (engine movement, heat)
• Sensor faulty internally
• Air or vapour bubbles at the sensor

What to check, in order

Start with the simplest. You can tick off each step.

1. With the engine cold, check the coolant level; never do this when the system is hot
2. Gently move the wiring with the engine running and watch whether the reading changes.
3. Check the actual temperature in live data
4. Make sure the fan comes on when it should
5. Check the thermostat and connector
6. Measure the sensor and replace it if its readings do not make sense

Good to know

• Repair difficulty: easy

What each character of P05C6 means

• P: Powertrain: engine and transmission
• 0: Generic code: same on every make
• 5: Speed and idle
• C6: Specific fault in that system

Frequently asked questions

Can I keep driving with code P05C6?

Watch the temperature gauge. If it climbs or a warning appears, stop the car in a safe place and turn off the engine: overheating can cause serious damage.

What causes code P05C6?

The most common causes are: loose contact or connector corrosion; chafed wire (engine movement, heat); sensor faulty internally.

Related codes

• P05C2Engine Coolant Pressure Sensor Circuit
• P05C3Engine Coolant Pressure Sensor Circuit Range/Performance
• P05C4Engine Coolant Pressure Sensor Circuit Low
• P0117Engine Coolant Temperature Sensor 1 Circuit Low
• P2560Engine Coolant Level Low
• P0217Engine Coolant Over Temperature Condition

Sources

• law.cornell.edu: 13 CCR 1968.2
• patents.google.com: US11815003
• patents.google.com: US10006337

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.