P0401 Weichai — EGR flow low, causes and repair

Fault codes / P0401

EGR flow is below command. On Weichai WP the valve often gums up on short trips.

Which trucks see it

WP10–WP13 Howo/Shacman, MC11 Sitrak. Cooler clogs too.

Symptoms

• MIL with decent pull
• black smoke
• rough idle hot

Likely causes

• Carbon-stuck EGR valve.
• Blocked EGR cooler.
• Position / delta-P sensor.

What to check

1. Command the valve with a scan tool.
2. Pull it and look at the pintle.
3. Check cooler hoses for coolant.
4. Do not just delete the code/map until the valve is understood.

Can you keep driving

You can drive. Fix it before it takes the turbo/DPF with it.

Look up the code in the service

Other codes

• P0087 — low common-rail pressure
• P0193 — rail pressure sensor high signal
• P0299 — boost below target
• P0335 — crankshaft sensor no signal
• U0100 — lost communication with engine ECU
• P0562 — system voltage low
• P0201 — cylinder 1 injector circuit
• P0116 — water in fuel (Weichai table) / not always coolant SAE
• P2509 — intermittent ECM power (no OEM in DB)