What it means
The dedicated supply voltage to the coolant pump module is above operating range. Wiring faults of this kind typically come from chafing, water ingress at connector seals, or pin push-back — a wiggle test on the harness while the code is active often confirms the location.
At a glance
- Usually lights the check-engine light
How it works
The dedicated supply circuit feeds the coolant pump control module. P26D5 specifically indicates voltage above the expected range, which may be caused by excessive charging voltage, a short to a higher-voltage circuit, or a faulty connector.
Common causes
Most likely first.
- Alternator regulator failed to limit output
- Wiring shorted to a higher-voltage circuit
- Connector pins corroded - high contact resistance
Symptoms
- Check-engine light may be on
- Engine temperature may rise or overheat
- Cooling-system warning may appear
How to diagnose it
- Check freeze-frame data and live module supply and battery voltage to see whether the high reading tracks charging-system operation.
- Inspect the dedicated supply harness and connector for damaged insulation, cross-contact with another power wire, corrosion, or loose pins.
- Test alternator output and regulation against the manufacturer's specification under the conditions in the freeze-frame data.
- If charging output is within specification, trace the supply wire for a short to a higher-voltage circuit using the wiring diagram.
- Check connector terminals and measure supply voltage at the module to distinguish a wiring fault from an upstream charging issue.
Common fixes
- Repair damaged supply-wire insulation or a short to a higher-voltage circuit.
- Clean or repair corroded or loose connector terminals.
- Repair or replace the alternator or regulator if output exceeds specification.
Can I keep driving?
High supply voltage may disrupt pump operation and can affect other electrical components, so avoid driving if a cooling warning or rising temperature appears. Stop safely if the engine overheats.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.