P0402 indicates the powertrain control module has detected exhaust gas recirculation (EGR) flow greater than expected for current operating conditions. This typically means the EGR valve is allowing too much exhaust gas into the intake manifold.
Carbon deposits or mechanical failure can cause the EGR valve to remain partially or fully open, allowing excessive exhaust flow.
Heavy carbon accumulation can prevent the valve from seating properly or alter flow dynamics, leading to higher-than-expected EGR flow.
A malfunctioning position sensor may report incorrect valve position, causing the PCM to misjudge flow.
A vacuum leak or short to voltage in the EGR solenoid circuit can hold the valve open longer than commanded.
On some vehicles, a faulty DPFE sensor can send erroneous flow signals to the PCM.
Internal PCM driver or processing fault is possible but extremely rare; only consider after all other causes are eliminated.
The definition is universal; the diagnostics are engine-specific. Open your vehicle for the codes documented for it:
No. PCM failure is an extremely uncommon cause of P0402. The code is almost always due to a mechanical issue with the EGR valve, carbon buildup, or a sensor fault. Replace the PCM only after thorough testing rules out all other causes.
Yes. Partial blockage can change pressure differentials across the valve, causing the PCM to calculate higher flow than actual, or prevent the valve from closing completely.
Often, yes. If carbon deposits are preventing the valve from closing fully, cleaning can restore proper operation. However, if the valve is mechanically damaged, replacement is required.
Driving with excessive EGR flow can cause rough idle, stalling, and increased emissions. Extended operation may lead to carbon buildup in the intake or damage to other components. Repair promptly.