DTC: P0400

Search Bulletins/Recalls for P0400

Trouble diagnosis name: EGR function

Component Description

Early Models: The EGR valve control the amount of exhaust gas routed to the intake manifold. Vacuum is applied to the EGR valve in response to the throttle opening. The vacuum control the movement of the taper valve connected to the vacuum diaphragm in the EGR valve.

Late Models: The EGR volume control valve uses a step motor to control the flow rate of EGR from exhaust manifold. This motor has four winding phases. It operates according to the output pulse signal of the ECM. Two windings are turned ON and OFF in sequence. Each time an ON pulse is issued, the valve opens or closes, changing the flow rate. When no change in the flow rate is needed, the ECM does not issue the pulse signal. A certain voltage signal is issued so that the valve remains at that particular opening.

DTC detecting condition:

• If the absence of EGR flow is detected by EGR temperature sensor under the condition that calls for EGR, a low-flow malfunction is diagnosed.
• When no EGR flow is detected under condition that calls for EGR.

Possible cause:

• Harness or connectors (EGR volume control valve circuit is open or shorted.)
• EGR volume control valve stuck closed
• Dead (Weak) battery
• EGR temperature sensor and circuit
• EGR passage clogged
• Exhaust gas leaks