DTC P0400 - Exhaust Gas RECIRCULATION (EGR) Flow Malfunction

1. Turn ignition on. If EGR valve stepper motor operates for 0.6 second, go to step 3). If operation is not as specified, go to next step.
2. Turn ignition off. Disconnect EGR valve harness connector. Turn ignition on. Using a voltmeter, measure voltage between Blue/Black wire terminals of connector and ground. If reading is 10-14 volts, go to next step. if reading is not as specified, repair open Blue/Black wire. Retest system.
3. Turn ignition off. Using a voltmeter, measure voltage (backprobe) between ground and PCM harness connector "D", terminals No. 7, 8, 9, then 10 as ignition is turned on. If reading is 4-8.4 volts for each terminal for 0.6 second, go to next step. If reading is not as specified, go to step 5).
4. Check for a stuck or faulty EGR valve. Check for clogged EGR passage in intake manifold. Repair as necessary. If EGR valve and passage are okay, replace PCM. Retest system.
5. Using an ohmmeter, check resistance of EGR stepper motor coils. See Fig 1 . Measure resistance between terminals "A" and "B", "C" and "B", "F" and "E", then "D" and "E". Resistance for each should be 20-24 ohms. If resistance checks okay, go to next step. If resistance is not as specified, replace EGR valve. Retest system.
6. Check for poor EGR valve harness connections at EGR and PCM. Inspect EGR valve harness for opens or shorts. Repair as necessary. If harness and connections are okay, replace PCM. Retest system.

Fig 1: Identifying EGR Valve Connector Terminals

Courtesy of SUZUKI OF AMERICA CORP.