What it means
The feedback line that confirms pump speed reads below the plausible range - either pump not turning or feedback line shorted to ground.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The EGR cooler coolant pump's feedback circuit reports whether the pump is turning, often through a speed signal. The control module sets P24AC when that feedback reads below the plausible range, which can mean the pump is not turning or its feedback wire is shorted to ground. The module may then be unable to confirm coolant circulation through the EGR cooler.
Common causes
Most likely first.
- Feedback line shorted to ground
- Connector pins corroded - high contact resistance
- Harness chafing through insulation
Symptoms
- Check engine light on
- Pinging or knocking under load
- Power loss and hesitation
- Possible rough idle
- Failed emissions inspection (NOx)
How to diagnose it
- Record freeze-frame data and compare pump command with available pump-speed feedback to see whether the low reading occurs while the pump is commanded on.
- Inspect the feedback-wire harness for chafing, damaged insulation, water ingress, or contact with ground.
- Check the pump connector for corrosion, a loose fit, or a pushed-back feedback terminal.
- With the circuit isolated and tested according to the manufacturer's procedure, check for a feedback wire short to ground and wiggle the harness while monitoring the signal.
- If the signal wire and connector are sound, check that the pump turns when commanded and test its feedback output and module input.
Common fixes
- Dry and clean the connector and restore a secure feedback-terminal fit.
- Repair feedback-wire insulation where it is rubbed through to ground.
- Replace a damaged or corroded feedback terminal.
- Replace the pump if it does not turn or its feedback output is faulty.
- Repair the control module if its feedback input is confirmed faulty.
Can I keep driving?
Avoid heavy-load driving until pump rotation and feedback are verified, since the module may not confirm coolant flow and the EGR cooler could overheat. Stop if knocking worsens or 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.