What it means
Same as P24A7 with the control line shorted to ground. EGR mixes inert exhaust into intake to lower combustion peak temperature — too little raises NOx, too much causes misfires and rough running.
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 circulates coolant to remove heat from exhaust gas passing through the EGR cooler. The control module monitors the pump control line and sets P24A9 when that line is held low, commonly by a short to ground, so the pump may not respond correctly. Loss of coolant flow can let the EGR cooler overheat.
Common causes
Most likely first.
- Control 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 check scan-tool pump command and feedback to determine whether the fault appears when the pump is switched on.
- Inspect the pump connector and harness for moisture, corrosion, rubbed insulation, or a wire trapped against ground.
- Check for a pushed-back or corroded control-line terminal that could create a poor connection.
- With the circuit isolated and tested according to the manufacturer's procedure, check whether the control line is shorted to ground and perform a careful harness wiggle test.
- If the control wire is not shorted and the pump checks out, test the control-module output and pump circuit using the manufacturer's procedure.
Common fixes
- Dry and clean the pump connector and restore a secure terminal fit.
- Repair insulation where the pump control wire is chafed against ground.
- Replace a damaged or corroded control-line terminal.
- Replace the EGR cooler coolant pump if it is pulling the control circuit low internally.
- Repair the control module if its output is confirmed faulty.
Can I keep driving?
Avoid towing, hard acceleration, and other heavy-load driving until the low control-line fault is fixed, since the pump may not circulate coolant and the EGR cooler can 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.