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DTC codes / P26xx · Computer and output circuits / P261C

P261CCoolant Pump B Control Circuit Low

P261C indicates that the powertrain control module (PCM) has detected a low-voltage condition on the control circuit for coolant pump B, which is often an auxiliary electric pump used for turbocharger or battery cooling. The PCM commands the pump on and monitors the circuit, and it sets this code when the voltage on the control wire falls below the expected threshold, indicating a short to ground or an open circuit.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaComputer and output circuits

Symptoms you may notice

  • Illumination of the check engine light, often with no other noticeable symptoms
  • The coolant pump may not run, leading to reduced cooling of the turbocharger or other components
  • Possible overheating warning or elevated coolant temperatures under heavy load
  • Reduced engine performance if the PCM enters a protective limp mode
  • A whining or humming noise from the pump area may be absent when the pump should be running
  • In some cases, the vehicle may stall or have difficulty restarting after a hot shutdown

Common causes, most likely first

  1. Faulty coolant pump B (electrical failure or seized pump)
  2. Open or shorted control wire between the PCM and the pump
  3. Corroded or damaged electrical connector at the pump or PCM
  4. Blown fuse or faulty relay supplying power to the pump circuit
  5. PCM internal fault causing incorrect voltage detection
  6. Poor ground connection for the pump circuit

How to diagnose and fix it

  1. Verify the battery voltage and condition, as a weak battery can cause false low-voltage codes
  2. Inspect the wiring harness and connectors at the coolant pump for damage, corrosion, or loose pins
  3. Check the fuse and relay that supply power to the coolant pump circuit
  4. Measure the control circuit voltage at the pump connector with the key on and engine off, comparing to specifications
  5. Command the coolant pump on with a scan tool and listen for operation, and check for voltage drop across the circuit
  6. If the circuit tests good, test the pump motor resistance and replace the pump if out of specification
  7. Clear the code and perform a road test to verify the repair, and check for any related codes that may indicate a PCM issue

Don't overlook the auxiliary coolant pump

  • P261C often sets intermittently due to a chafed wire that only shorts when the engine moves, so a wiggle test of the harness is essential.
  • A failing auxiliary coolant pump may not trigger overheating symptoms until the vehicle is driven hard, leading owners to ignore the code.
  • The PCM may set P261C if the pump connector is unplugged, so always check for a disconnected plug before condemning the pump.
  • Some vehicles use the auxiliary pump for cabin heating or battery thermal management, so a fault may cause poor heater performance rather than engine overheating.
  • A shorted pump motor can damage the PCM driver, so replacing only the pump without checking the control circuit may lead to a repeat failure.

Can I keep driving with P261C?

It is generally safe to drive short distances to a repair shop, but avoid heavy loads, towing, or aggressive driving that increases heat, as the auxiliary pump may be needed for cooling. If the engine temperature gauge rises or a warning light appears, stop and shut off the engine.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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