The engine control module (ECM) performs a flow test on the exhaust gas recirculation (EGR) system during deceleration. The ECM does this by momentarily commanding the EGR valve to open while monitoring the signal of the manifold absolute pressure (MAP) sensor and the EGR position sensor. If the MAP signal is incorrect for the EGR pintle position, the ECM records the amount of MAP difference that was detected and adjusts a calibrated fail counter towards a calibrated fail threshold level. The number of EGR flow tests required to exceed the fail threshold may vary according to the amount of detected EGR flow error.

Normally, the ECM will only allow one EGR flow test during an ignition cycle. To aid in verifying a repair, the ECM will allow multiple EGR flow tests following a code clear event.

P0400

The MAP changes monitored by the ECM during the EGR flow tests indicate an incorrect amount of EGR flow.

P0402

The MAP changes monitored by the ECM during the EGR flow tests indicate an excessive amount of EGR flow.

P1402

The MAP changes monitored by the ECM during the EGR flow tests indicate an insufficient amount of EGR flow.

DTCs P0400, P0402, and P1402 are type B DTCs.

DTCs P0400, P0402, and P1402 are type B DTCs.

Schematic Reference

Engine Controls Schematics

Description and Operation

Exhaust Gas Recirculation (EGR) System Description

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

1. Engine running, observe the DTC Information with a scan tool. Verify that DTC P0107, P0108, P0400, P0402, P0403, P0404, P0405, P0406, or P1402 is not set.

⇒	If any of the DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle for further diagnosis.

2. Observe the DTC Information with a scan tool. DTCs P0400, P0402, or P1402 should not set.
3. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

1. Verify none of the following conditions exist:

•	Incorrect EGR valve for engine application

•	A vacuum leak between the EGR valve and the intake manifold

•	Signs of external leakage usually indicated by carbon buildup around the mating surfaces of the components or an audible exhaust noise

•	Restrictions in the passages or EGR valve caused by carbon deposits or casting flash

•	Leaks or restrictions at the MAP sensor

Important: Restrictions can cause excessive back pressure and low engine vacuum.

•	Leaking, restricted, or modified exhaust system--Refer to Symptoms - Engine Exhaust .

•	Mechanical failure in the engine such as worn piston rings, camshaft or incorrect timing belt installation--Refer to Symptoms - Engine Mechanical .

2. If all conditions test normal, test or replace the EGR valve.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Exhaust Gas Recirculation Valve Replacement