P0402 — Exhaust Gas Recirculation Flow Excessive
P0402 sets when EGR flow is higher than commanded, usually a valve stuck open or sensor reporting incorrect position. Commanded-closed test with MAP/MAF confirmation isolates a stuck valve before sensor or ECM replacement.
Fault Overview
EGR valve stuck open from carbon or mechanical failure, position sensor bias, control circuit short, failed actuator, and incorrect adaptations are the primary causes. Stuck-open EGR causes rough idle, black smoke, and low power. Carbon can hold the valve off its seat even when the actuator is good.
Engine & Platform Coverage
Symptoms
- •P0402
- •EGR flow excessive
- •EGR stuck open
- •excessive EGR diesel
- •rough idle EGR
Possible Causes
- 1.EGR valve stuck open (carbon or mechanical)
- 2.Position sensor bias
- 3.Control circuit short
- 4.Failed actuator
- 5.Incorrect adaptations
Wiring & Circuit Notes
EGR control and position circuits for short-to-power or driver faults.
DVOM Specs & Sensor Tests
Actual position at closed command. MAP/MAF with valve commanded closed. Valve movement freedom.
Diagnostic Flow — FSM Sequence
AI Diesel Tech enforces this evidence-gate sequence. Each gate must pass before advancing.
4 steps locked behind Technician Mode- 1Step 1 — Command EGR Closed and Monitor Position and MAP/MAF: Command the EGR valve fully closed and monitor position feedback and MAP/MAF. If MAP/MAF still shows EGR flow, the valve is not closing.
- 2Step 2 — Remove and Inspect Valve for Carbon Holding It Open: Remove and inspect the EGR valve for carbon deposits holding it off its seat.
- 3Step 3 — Check Position Sensor Circuit: Check the position sensor circuit for bias or short-to-power that could falsely indicate an open valve.
- 4Step 4 — Verify Control Circuit Is Not Forcing the Valve Open: Verify the control circuit is not forcing the valve open due to a short or driver fault.
- 5Step 5 — Clean or Replace Valve and Retest: Clean or replace the EGR valve and perform adaptations. Retest with commanded-closed verification.
Unlock the full evidence-gated diagnostic sequence, DVOM test steps, and repair procedures in Technician Mode.
Full Diagnostic Access
Verification steps, preventative measures, severity guidance, and legacy comparison are available in Technician Mode.
Typical Repair Costs
Clean or replace EGR valve $200–600; repair circuit $100–300; perform adaptations $50–150.
Related Codes & Pages
Start Diagnosing This Fault Now
AI Diesel Tech walks you through every evidence gate in the correct order. Choose the plan that fits your shop.
AI Diesel Tech — The Technician's Diagnostic Engine
AI Diesel Tech diagnostic logic is built by an ASE Certified Diesel Technician and engineered for professional shop use. Trusted by technicians nationwide — used in shops, fleets, and training programs.
Summary
Use the AI Diesel Tech diagnostic engine to run this code through a structured, evidence-gated sequence and get a confirmed root cause before any parts are replaced.