P2C66

Code

Generic P — Powertrain

Hybrid/EV Electronics Coolant Pump A Underspeed

Brand: Generic

Type: P — Powertrain

Views: UK: 18 EN: 21 RU: 19

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Page language: EN

Causes

Wiring or connector fault to the pump (open, high resistance, corrosion, damaged pins)
Low supply voltage or poor ground to pump or pump driver
Faulty pump motor (worn brushes, damaged rotor, internal electrical fault)
Pump partially seized, obstructed impeller, air lock or low coolant level
Faulty pump driver / inverter or control module output stage
Incorrect PWM command (ECU/software fault) or sensor feedback error

Symptoms

DTC P2C66 stored, possible freeze frame data showing low pump speed
Warning on instrument cluster (EV/hybrid coolant or inverter temperature message)
Inverter / power electronics running hotter than normal or entering limp modes
Reduced climate cooling performance (if same circuit)
Unusual noise from pump (grinding, rubbing) or no audible pump activity

What to check

Read and record freeze frame and live data (pump commanded speed/PWM, actual speed, supply voltage, motor current)
Check for related DTCs (cooling, HV system, pump driver, power distribution)
Visual inspection: connectors, harness for damage, chafing, corrosion; inspect fuses and relays
Verify coolant level and look for air pockets in cooling circuit; inspect for blocked hoses or debris at pump inlet
Listen for pump operation when commanded (apply command in safe test mode)
Measure voltage at pump connector while commanded (engine off / HV disabled where applicable) and during command; measure ground integrity

Signal parameters

Command parameter: PWM duty or requested speed — should match commanded value within tolerance (typical tolerance ±10–20%)
Actual pump speed: RPM or percent of commanded; underspeed fault if significantly below command
Supply voltage: should be within vehicle spec during command (no significant drop under load)
Motor current: expected nominal current vs stall current (low current may indicate open winding/weak motor; high current indicates mechanical bind)
PWM frequency: specified frequency for pump driver (consult vehicle data); abnormal frequency may indicate driver fault

Diagnostic algorithm

Retrieve codes and freeze frame; note operating conditions when fault occurred (temperature, state of charge, vehicle mode).
Check for other codes that may point to driver/ECU faults. If present, address those first.
Perform visual inspection: wiring, connectors, fuses, relays. Repair any obvious damage or corrosion.
Confirm coolant level and bleed air from circuit if required. Re-test with correct coolant level.
With appropriate HV safety measures in place, command pump ON from diagnostic tool and observe: listen for pump, watch live data for commanded vs actual speed, record supply voltage and motor current.
Measure voltage and ground at pump connector while commanded. High resistance in supply/ground will show voltage drop under load.
Probe PWM command at pump (or driver input) with scope or appropriate tool to confirm correct duty cycle and frequency from the control module.
Measure motor current during operation. Compare to expected values. Low current with low speed suggests motor or open winding; high current with low speed suggests mechanical bind.
If electrical signals from controller are correct and supply is good, remove pump and bench-test or replace with known-good unit to confirm mechanical/electrical pump condition.
If pump is good, test/replace pump driver or repair control module outputs per manufacturer procedures; update software if TSB exists.
After repairs, clear codes and perform system functional test and road/operational test to confirm no return of fault.
Safety: follow high-voltage isolation and lockout/tagout procedures when working on HV components; if unsure, refer to manufacturer HV service documentation.

Likely causes

High-resistance connection at pump power/ground causing reduced voltage under load
Mechanical obstruction or binding in pump reducing actual speed
Faulty pump motor that draws low current or slips under load
Pump driver transistor or MOSFET partially failed reducing available current to motor