P0402 — Exhaust Gas Recirculation Flow Excessive — 6.0 Power Stroke

Diagnostic reference for 6.0 Power Stroke (2003.5–2007) EGR flow excessive.

Updated October 15, 2026

What it means

P0402 is generic for measured EGR flow higher than commanded. On the 6.0L Power Stroke this is most often an EGR valve stuck partly open with soot, which can cause rough idle, black smoke or stalling.¹

Most likely causes

1. EGR valve stuck partly open from soot buildup — The electronically controlled EGR valve with position sensor can stick open due to soot, causing flow higher than commanded. Typical on this platform for excessive EGR flow.¹
2. EGR valve position sensor / control circuit performance issue — The EGR valve may not reach commanded position within expected range/time due to soot sticking or electrical issues. On the 6.0L this is typically a sticking EGR valve from soot build-up; check connector and wiring before condemning the valve.²
3. EGR cooler restriction or failure affecting flow balance — A restricted or failed EGR cooler can alter EGR flow characteristics. On the 6.0L low EGR flow is usually a soot-stuck EGR valve or a restricted EGR cooler; if there is also coolant loss or white steam from the exhaust, suspect a failed EGR cooler often caused by a clogged engine oil cooler.³
4. Excessive exhaust back pressure influencing EGR operation — EBP sensor/tube issues can affect VGT control and indirectly EGR operation. The 6.0L EBP sensor reads exhaust manifold pressure through a steel tube and is used for VGT control; wiring/connector faults or a failed sensor are typical, and a soot-clogged EBP tube more often sets P0471.⁴

How to diagnose

1. Verify code P0402 is present and check for related EGR codes P0401, P0404, P1335.
2. Inspect EGR valve operation and soot accumulation; look for valve stuck open or slow response.
3. Check EGR valve electrical connector and wiring for damage or corrosion.
4. Inspect EGR cooler for signs of coolant loss, white steam/smoke from exhaust, or overheating; note that EGR cooler rupture can lead to loss of coolant, white smoke exiting exhaust, engine overheating, and can lead to blown head gaskets.
5. Assess engine oil cooler health; EGR cooler failure is usually caused by a clogged engine oil cooler.
6. Check exhaust back pressure sensor and steel tube for soot clogging or wiring faults that could affect EGR control.

Specs and test values

Common mistake to avoid

Replacing a failed EGR cooler without checking the oil cooler. A restricted oil cooler cuts coolant flow to the EGR cooler, which then overheats and cracks again. Compare oil and coolant temperatures (EOT vs ECT) before the repair. Source: Bulletproof Diesel — 6.0 Powerstroke oil cooler symptoms.

Parts and tools you may need

• Scan tool with Ford enhanced diagnostics
• Digital multimeter
• Inspection light
• Borescope for EGR passages

Tools you’ll need

• digital multimeter — Checks EGR valve position sensor voltage and control circuit continuity to rule out electrical faults causing high flow readings.
• OBD-II scan tool — Reads P0402 and related EGR codes and monitors live EGR valve position vs commanded to confirm excessive flow.

Rough cost and difficulty

Typical US independent-shop figures; labor runs about $120–$180 per hour (dealers charge more). Confirm the diagnosis before buying parts.

When to see a pro

If diagnosis indicates EGR cooler rupture, head gasket concerns, or requires internal engine work, have a qualified diesel technician evaluate the vehicle. Do not perform step-by-step repair of safety-critical systems. NHTSA reports document loss of coolant, white smoke, overheating leading to blown head gaskets, and EGR/oil cooler failures requiring replacement.

Check for recalls

Recalls are tied to your truck’s VIN, so check yours directly: enter the VIN at NHTSA’s recall lookup. Open safety recalls are repaired free at a dealer.

Sources