P2B68

Code

Generic P — Powertrain

Coolant Pump D Control Circuit High

Brand: Generic

Type: P — Powertrain

Views: UK: 26 EN: 26 RU: 18

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Page language: EN

Causes

Short to battery / high reference voltage on coolant pump D control wire
Failed coolant pump (internal short or shorted driver inside pump module)
Open or high resistance ground in pump circuit
Corroded/damaged connector or wiring (intermittent short/high resistance)
Faulty ECM / pump driver transistor (less common)
Relays/fuses or secondary control module stuck closed or supplying voltage when not commanded

Symptoms

Malfunction Indicator Lamp (MIL) or coolant-warning lamp illuminated
Erratic or continuous operation of coolant pump D (runs when it should be off or fails to run when commanded)
Possible coolant temperature control problems (overheating or running too cool)
Battery drain when vehicle is off (if circuit stuck powered)
Intermittent faults or drivability complaints related to coolant temperature

What to check

Read and record freeze frame and freeze data with a scan tool; note operating conditions when the code set
Visually inspect harness and connectors at the coolant pump, ECM and any intermediate modules for corrosion, damage, pin push-out or water intrusion
Check related fuses and relays for correct operation and correct part number
Backprobe control connector with a DVOM/oscilloscope while commanding pump ON and OFF from a scan tool
Check for other related DTCs (coolant pump, fan, temperature sensors) to help narrow fault location
Wiggle harness and connectors while monitoring control voltage and DTC status to reproduce intermittent faults

Signal parameters

Nominal battery voltage: 12.0–14.8 V (engine running)
Expected control voltage when pump should be OFF: ~0 V (or open circuit depending on design)
Expected control voltage when pump should be ON: switched or PWM between 0–battery voltage (0–14.8 V)
Typical PWM frequency (if used): commonly 20–200 Hz (vehicle-specific)
Normal pump coil resistance (approximate): 1–10 Ω (varies by pump)
Typical operating current: 0.5–10 A depending on pump size; check vehicle spec

Diagnostic algorithm

Retrieve freeze frame and DTC history with a scan tool; record engine temp, voltage, and operating state when code set
Visually inspect wiring and connector at Coolant Pump D. Repair any obvious damage or corrosion.
With ignition ON (engine off), backprobe the control pin at the pump connector and measure voltage. Command the pump ON/OFF with a scan tool and observe voltage change.
If the circuit reads high voltage when pump is commanded OFF, disconnect the pump connector and measure voltage at the harness side. If the voltage returns to expected (low), suspect pump internal short or short to power in the pump assembly.
If the harness still reads high with pump disconnected, trace wiring toward the ECM looking for short to battery, damaged insulation, or a stuck relay supplying constant power.
Measure continuity/resistance from control pin to ECM and to ground as applicable. Check for unintended continuity to battery positive.
Bench-test the pump by applying fused battery power directly to the pump ground and positive to confirm pump operation and current draw. Compare measured current to manufacturer specs.
If harness and pump check OK, use an oscilloscope to check ECM output waveform while commanding the pump. If the ECM output is abnormal and wiring/pump are good, consider ECM repair/replacement as last step.
Clear codes and perform a road or functional test to confirm repair. Monitor related systems and verify no additional DTCs return.

Likely causes

Short to power on the pump control lead (wiring pinched or chafed)
Failed pump with internal short or incorrect internal electronics
Bad ground connection at pump or harness ground point
Corroded connector or poor pin contact causing abnormal voltage reading
Faulty ECM output stage (verify after harness/pump checks)

Fault status

⚠️ Status

Control circuit for Coolant Pump D is reporting voltage higher than expected. The ECM detected an over-voltage condition on the pump control circuit and set DTC P2B68. Inspect wiring, connectors, pump, fuses/relays; replace or repair component as indicated by diagnostics.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-3.0 hours