Code
P2B66
Generic
P — Powertrain
Coolant Pump D Control Circuit/Open
AI status
Completed
Completed
100%
Causes
- Open or shorted wiring in the coolant pump D harness
- Corroded, loose or damaged connector at the pump or module
- Blown fuse or faulty relay supplying the pump circuit
- Failed coolant pump motor (open winding or internal failure)
- Faulty powertrain control module (driver stage) or internal MOSFET
- Poor ground connection
Symptoms
- Malfunction Indicator Lamp (MIL) illuminated
- Possible engine overheating or temperature rise if pump inoperative
- Reduced heater performance or HVAC temperature issues
- Cooling system warnings on dash
- No audible pump noise when pump is commanded
What to check
- Connect a scan tool, read freeze frame and DTC status, note any related codes
- Use actuator/bi-directional test to command Coolant Pump D ON/OFF and observe response
- Visually inspect pump harness, connector, and pin condition for corrosion or damage
- Check relevant fuses and relays for continuity and proper operation
- Backprobe harness at pump and at module to verify voltage supply, ground and control signal while commanding
- Measure resistance of pump motor (with connector disconnected) and compare to OEM specs
Signal parameters
- Expected supply voltage at pump: near battery voltage (~11–14.5 V) with key ON/engine running (varies by design)
- Control output type: usually low-side switching or PWM from ECM; voltage swings between ~0 V and battery voltage or a PWM duty signal
- Commanded duty cycle: 0–100% depending on requested pump output (scan tool should show commanded percent)
- Typical PWM frequency (generic range): tens to a few hundred Hz (consult OEM data for exact frequency)
- Pump motor resistance: varies by design — measure and compare to OEM specification
Diagnostic algorithm
- Safety: park vehicle on level ground, set parking brake, wear eye protection. Allow engine to cool before working near cooling system.
- Verify code: connect a scan tool, confirm P2B66 is active or stored, record freeze-frame data and any related codes.
- Attempt actuator test: command Coolant Pump D ON via scan tool and observe whether pump runs (audible/vibration) and whether engine parameters change. Note whether code reappears.
- Check fuses/relays: visually inspect and test continuity of any fuse/relay protecting the pump circuit. Replace suspected faulty items and retest.
- Visual/wiggle inspection: inspect harness from pump to module for chafing, broken wires, or damaged connectors. Wiggle harness while commanding pump and watch for intermittent operation.
- Backprobe and measure: with connector connected, backprobe the pump power and control pins. With key ON and during commanded ON, verify battery supply at power pin and that the control pin switches (to ground or battery) as commanded. Compare readings to signal expectations.
Likely causes
- Broken or disconnected connector at coolant pump D
- Open wire or broken conductor between ECM and pump
- Blown fuse or failed relay in pump supply
- Pump motor has an open coil (failed pump)
- ECM output transistor for pump D failed
Fault status
Status
Coolant Pump D control circuit detected open or no response — ECM commanded pump but circuit returned no valid signal/feedback.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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