P2B6D: Engine Coolant Flow Control Valve Position Sensor Circuit Intermittent/Erratic

P2B6D covers a position signal from the engine coolant flow control valve that drops out or jumps for short moments, even though single readings may still lie inside the valid window. This exact code appears in no public manufacturer document. In GM's 3.0 L Duramax diesel the valve sends its angle digitally via SENT; the engine computer tests that sensor for a low reading (P2B5E, under 2 %), a high reading (P2B5F, over 98 %) and plausibility (P2B60, more than 12 % deviation) and treats lost SENT communication as a separate fault, but names no intermittent code. A system using P2B6D would count unstable readings, for instance from a loose terminal, fretting corrosion or a harness that moves with the engine. Input faults of this kind must be caught according to CARB 13 CCR 1968.2 (e)(15). Coolant flow control becomes unreliable.

Symptoms

• Warning lamp, code often stored as intermittent
• Temperature display or warm-up behaviour fluctuates

Most likely causes

• Loose or widened terminal in the valve connector
• Fretting corrosion on the signal or reference pins
• Harness rubbing or flexing with engine movement
• Position sensor inside the valve unstable

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: medium
• It affects emissions.

What each character of P2B6D means

• P: Powertrain: engine and transmission
• 2: Generic code: same on every make
• B: Subsystem depends on the code range
• 6D: Specific fault in that system

Frequently asked questions

Can I keep driving with code P2B6D?

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 P2B6D?

The most common causes are: loose or widened terminal in the valve connector; fretting corrosion on the signal or reference pins; harness rubbing or flexing with engine movement.

Related codes

• P2B5DEngine Coolant Flow Control Valve Position Sensor Circuit
• P2B5EEngine Coolant Flow Control Valve Position Sensor Circuit Low
• P2B5FEngine Coolant Flow Control Valve Position Sensor Circuit High
• P2B60Engine Coolant Flow Control Valve Position Sensor Circuit Range/Performance
• P2B61Engine Coolant Flow Control Valve Stuck Closed

Sources

• gsi.ext.gm.com: 25OBDG04B
• law.cornell.edu: 13 CCR 1968.2

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.