P0402 Code: Exhaust Gas Recirculation (EGR) Flow Excessive Detected
More exhaust is being recirculated than the ECU asked for, usually because the EGR valve won't fully close.
At a glance
Severity: Moderate
- Meaning
- Exhaust Gas Recirculation (EGR) Flow Excessive Detected
- System
- Emission Controls · Powertrain
- Safe to drive?
- With caution
- Typical repair cost
- $60–$750
- DIY difficulty
- Moderate
At idle and during deceleration the EGR valve is supposed to be shut tight, because exhaust gas in a slow-running engine only dilutes the mixture and makes combustion unstable. P0402 means the ECU saw evidence of EGR flow when it wanted little or none, or noticeably more flow than it commanded. On many Fords that evidence comes from the DPFE pressure sensor, on GM trucks from the pintle position sensor, and on other engines from manifold pressure or fuel trim. The usual story is a piece of carbon wedged under the valve seat, a vacuum solenoid that bleeds vacuum to the valve all the time, or a feedback sensor that falsely reports flow.
Can I keep driving? Drive carefully: a valve that is hanging open can make the engine stumble or stall when you slow down or stop at a light, which is a hazard in traffic. Keep the idle a little higher when coming to a stop and get it diagnosed soon.
How to read P0402
- P Powertrain
- 0 Generic (SAE)
- 4 Auxiliary emission controls
- 02 Specific fault
Symptoms
- Check engine light on
- Rough, shaky idle that smooths out once you drive off
- Engine stalls when coming to a stop or when the A/C kicks on
- Hesitation or bucking at light throttle
- Hard starting after the engine has been warmed up
- Strong exhaust smell and sometimes a fuel-trim or misfire code alongside
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Carbon flake or deposit holding the EGR valve slightly off its seat
- EGR vacuum solenoid leaking vacuum to the valve, or hoses routed incorrectly after a repair
- Faulty DPFE sensor or its two hoses reversed or cracked (Ford)
- Electronic EGR valve stuck partly open or its position sensor reading too high
- MAP sensor or vacuum leak skewing the ECU's flow calculation
- ECU software or driver fault keeping the valve commanded open
Diagnosis step by step
Watch EGR data at a warm idle
With the engine fully warm, look at EGR commanded versus actual position, or at the DPFE voltage on Fords. At idle the command should be 0% and the actual reading at its closed baseline; any reported flow here is the problem in a nutshell.
Tools: OBD-II scanner
Check for vacuum at the valve at idle
On vacuum-operated valves, tee a gauge into the line at the valve. At a warm idle it should read zero; if it shows vacuum, the control solenoid is leaking through or someone connected the valve straight to manifold vacuum.
Tools: Vacuum gauge
Try the pinch-off test
Disconnect and plug the vacuum hose to the EGR valve, or unplug an electric valve, and see if the idle smooths out. If the idle stays rough with the valve unpowered, the valve is mechanically stuck open by carbon rather than being told to open.
Tools: Pliers
Check the DPFE sensor and hoses (Ford)
With the key on and engine off, the DPFE signal should sit near its baseline, typically under about 1 V. A higher reading suggests a failed sensor; also check that each hose goes to the port marked on the sensor body (the two hoses usually differ in diameter) and that neither is cracked or melted.
Tools: Multimeter, Flashlight
Pull the valve and inspect the seat
Remove the valve and look for a carbon chunk on the pintle or seat, and try to close it by hand. Clean the seat and the port opening; if the pintle is bent or the seat face is pitted, the valve won't seal and needs replacing.
Tools: Screwdriver, Flashlight, Gloves
Clear the code and verify at idle and cruise
After the repair, clear the code and let the engine idle warm for several minutes, then drive with some stop-and-go and steady 40–55 mph cruising. The idle should be smooth and the EGR monitor should complete without a pending code.
Tools: OBD-II scanner
Where the parts are
- 1MAF sensor
- 2Turbocharger
- 3Throttle body
- 4Intake manifold
- 5Fuel injector
- 6EGR valve
- 7Fuel pump
- 8Thermostat
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Clean EGR valve seat and port | Yes | $120–$350 |
| Replace DPFE sensor and hoses (Ford) | Yes | $90–$250 |
| Replace EGR vacuum solenoid or correct hose routing | Yes | $60–$220 |
| Replace EGR valve | No | $250–$750 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Notes by brand
Ford
On older Ford trucks and cars with the DPFE system, P0402 very often comes from a failed DPFE sensor or its hoses being installed on the wrong ports. Replacing the inexpensive sensor together with new heat-resistant hoses is the typical fix, but check that the EGR valve itself closes before buying parts.
Field data
| Ram | 2 | 1500 |
|---|
Source: NHTSA Complaints API (US government open data), analyzed by DTC mention.
Emissions / smog test impact
Will fail
An active P0402 with the check engine light on fails any OBD-based smog check. After the fix, the EGR monitor must show 'ready' again before the retest, which usually takes a few days of mixed driving.
Frequently asked questions
Why does my engine stall at stops with P0402?
At idle the engine gets very little fresh air, so even a small amount of exhaust leaking past the EGR valve dilutes the mixture enough to make it misfire or die. At higher speeds there's so much airflow that the same leak hardly matters.
Could it be my DPFE hoses instead of the valve?
Yes, on Fords that's one of the first things to check. If the two hoses are reversed or one is cracked, the sensor reads a pressure difference that doesn't exist and the ECU concludes there's too much flow.
Is P0402 the opposite of P0401?
Essentially yes. P0401 means too little flow and usually points to clogged passages; P0402 means too much flow and usually points to a valve that isn't closing or a sensor that falsely reports flow.
Can I unplug the EGR valve to stop the stalling?
Unplugging only helps if the valve is being commanded open; a carbon-jammed valve stays open anyway. It also sets more codes and fails the smog check, so treat it as a short test, not a fix.
Sources
- SAE J2012 – Diagnostic Trouble Code Definitions
- ISO 15031-6 – Road vehicles, diagnostic trouble code definitions (EOBD)
- US EPA – On-Board Diagnostics (OBD) program
- Manufacturer public service information (cross-checked)
- NHTSA Complaints API
- Methodology: How We Build Code Pages · Data Sources We Use · Editorial Policy