P2D08

Code

Generic P — Powertrain

Motor Electronics Coolant Pump B Supply Voltage Circuit

Brand: Generic

Type: P — Powertrain

Views: UK: 17 EN: 29 RU: 22

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Page language: EN

Causes

Blown fuse or faulty relay for coolant pump B supply
Open or shorted power supply wire to pump B (damage, chafing, corrosion)
Poor or corroded connector or terminal at pump B
Short to ground or short to battery in the pump supply circuit
Faulty coolant pump B (internal short/open)
Faulty ECM/driver transistor controlling pump B

Symptoms

Coolant pump B fails to run when commanded
Engine or battery thermal system warnings (temperature gauge, message)
Reduced cooling performance or elevated temperatures under load
Illuminated MIL/ warning lamp and recorded DTC
Unusual battery drain if short to battery exists
Intermittent operation or codes that clear then return

What to check

Read freeze frame and live data with a scan tool; confirm current status and if pump B is being commanded
Visually inspect fuse(s) and relay(s) related to the pump supply; replace if blown or suspect
Visually inspect wiring harness, connector(s) and pins at pump B for corrosion, bent pins, loose terminals or damage
Measure battery voltage at pump B power terminal with ignition ON and with engine running
Check continuity and resistance of supply and ground circuits to the pump (with battery disconnected when appropriate)
Measure pump coil resistance (spec) and current draw while commanded on

Signal parameters

Battery voltage at pump connector: ~12.0 V (key on, engine off) or ~13.5–14.5 V (engine running with alternator charging)
Pump coil resistance: typically low (manufacturer-specific); expect a few ohms to tens of ohms — consult service data
Pump current draw when running: nominal range depends on pump (commonly 1–10 A); excessive current suggests internal short or mechanical binding
Control signal: PWM or switched 12 V feed from ECM/relay; duty cycle/frequency per vehicle design
ECM output voltage on driver pin: should switch to supply voltage or PWM when commanded
Voltage drop across connectors/wiring: should be minimal (

Diagnostic algorithm

Retrieve DTC details and freeze frame using a scan tool. Note conditions when the code set (engine temp, battery voltage, vehicle speed, command state).
Visually inspect fuse(s), relay(s) and wiring for the pump B supply. Replace any suspect fuses/relays and reseat connectors.
With ignition ON, measure battery voltage at the pump B power pin and at the ECM/relay output pin. Compare values and look for excessive voltage drop.
Command pump B ON with a scan tool and observe supply voltage, control signal and whether the pump runs. If commanded and no operation, check for fused feed or relay control.
Measure pump coil resistance with battery disconnected. If open or shorted (out of spec), replace pump.
Measure current draw while pump is commanded ON. Excessive current indicates internal pump fault or short; no current indicates open circuit or fuse/relay/driver failure.
Perform continuity checks on supply and ground circuits between pump connector and ECM/relay. Repair any open or high-resistance cuts.
If wiring and pump check good, test ECM driver output for proper switching/PWM. If driver does not switch but command is present, suspect ECM fault and verify with manufacturer procedures before replacement.
If safe and practical, apply fused 12 V direct to the pump ground/power (bench or at vehicle connector) to verify pump mechanical operation. Use a fuse to prevent damage and observe current draw.
Clear codes and test drive/retest to confirm repair. If code returns, follow manufacturer-specific advanced diagnostics for ECM or harness repair.

Likely causes

Blown fuse or bad relay protecting the pump circuit
Open/poor connector or corroded terminal at the pump
Wiring damage (chafed, pinched) causing open or short
Failed pump motor drawing abnormal current or open circuit
ECM driver failure (less common)

Fault status

⚠️ Status

Supply voltage abnormal in Motor Electronics Coolant Pump B circuit — open, shorted, or out-of-range voltage detected. Check fuse, wiring, connectors, pump, and ECM driver.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours