P0E50: Motor Electronics Coolant Pump B Control Circuit Intermittent/Erratic
What to do
Expect power to fade on long climbs or when towing, and to recover after a rest. It is drivable. Worth fixing before it fails completely — an intermittent pump circuit is usually a pump or connector on its way out, and the electronics it cools are far more expensive than it is.
What this code means
The control circuit for one of the motor electronics coolant pumps is intermittent.
This is another family the standard split across blocks — the rest of this pump's codes were allocated in an earlier range, and only the Intermittent/Erratic variant landed here, added later. Two codes hundreds of numbers apart, same pump, no marker saying so; the corpus cross-links them because a scan tool will not.
The pump cools the power electronics rather than the battery, and the distinction matters because the symptoms differ. A battery cooling fault shows up as charging and range. This one shows up as power fading under sustained load — a long climb, towing, repeated hard acceleration — because the inverter derates when it cannot shed heat.
Intermittent is the hardest variant and the most informative. A pump circuit that fails intermittently is nearly always mechanical: a connector that has lost its spring tension, a chafed conductor, or a motor with a worn commutator that breaks contact as it turns. It is found by moving the harness with the reading live and by watching the pump's feedback while the car is hot — not by measuring resistance at rest, which is exactly when the fault is absent.
A pump that is failing this way usually stops altogether within weeks, so an intermittent code here is a warning worth acting on rather than a nuisance to clear.
Likely causes
Start here
- Faulty inverter coolant pump · specialist
- Corroded or loose connector · specialist
- Intermittent wiring fault · specialist
Less common
- Damaged wiring harness · specialist
- Control module driver failure · specialist
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
Be the first to write this up
Nothing posted about this yet. Whatever you found is worth writing down — even a dead end saves someone the same afternoon.
What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
Sign in or create an account to add what you found about P0E50.