Mazda MX-6 1998, Workshop Manual

Page: 82 / 1282

TROUBLESHOOTING [ENGINE CONTROL FS]
DTC P0400 EGR flow malfunction
DESCRIPTION • DTC P0400 indicates an EGR valve/flow failure
[Possible Cause]
• Damaged EGR valve • Damaged PCM
• Damaged EGR boost sensor • Damaged harness connector
• Damaged EGR boost solenoid valve • Damaged harness
• Restriction in exhaust system
STEP INSPECTION ACTION
1 OUTPUT ALL DTCS
• Verify EGR boost solenoid valve
connection and repair as necessary.
• Output all continuous memory, KOEO and
KOER self-test DTCs.
sy 0 1 -0 1 A ENGINE ON-BOARD
DIAGNOSIS [FS], Rettieving DTCs
Procedure
• Are any other DTCs displayed on NGS
tester?
Yes Go to DTC charts and PROCEED as required.
No Go to next step.
2
CHECK FOR UNMETERED AIR LEAKS
• Carefully inspect following areas for
potential air leaks:
• Hoses connecting to MAF sensor
assembly.
• Hoses connecting to throttle body.
• Intake manifold gasket leaks.
• Positive crankcase ventilation (PCV)
disconnected.
• Vacuum lines disconnected.
• Improperly seated engine oil dipstick
and tube.
• Exhaust leaks at flanges and gaskets.
• Are there any air leaks?
Yes Air leaks located.
SERVICE source of air leak.
RESET PCM to completely clear DTCs.
tr After Repair Procedure
COMPLETE OBD II Drive Mode.
RERUN OBD Test.
No Go to next step.
3 CHECK CYLINDER COMPRESSION
• Check cylinder compression.
o - 0 1 -1 0 A COMPRESSION INSPECTION
[FS]
• Are cylinder compression readings
within specification?
Yes Go to next step.
No SERVICE as necessary.
RESET PCM to completely clear DTCs.
c r After Repair Procedure
COMPLETE OBD II Drive Mode.
RERUN OBD Test.
4 CHECK OPERATION OF EGR VALVE
• Key on and listen for initialization noise
(clicks) of EGR valve by using screwdriver
or soundscope.
Note
• EGR valve initialization is closing action of
valve observed before and after engine is
started, and when engine is stopped.
• Does EGR valve initialization noise
heard?
Yes Go to step 9.
No Go to next step.
5
CHECK POWER CIRCUIT TO EGR VALVE
• Key off.
• EGR valve disconnected.
• Key on, engine off.
• Measure voltage between power circuit
and chassis ground at EGR valve vehicle
harness connector.
• Is EGR valve power voltage greater than
10.5 volts?
Yes Go to next step.
No SERVICE open in EGR valve power circuit.
RECONNECT all components.
RESET PCM to completely clear DTCs.
vt
After Repair Procedure
COMPLETE OBD II Drive Mode.
RERUN OBD Test.
6 CHECK RESISTANCE OF EGR VALVE
• Key off.
• EGR valve disconnected.
• Measure resistance of EGR valve coils.
• Is each resistance approximately 22
ohms?
Yes Go to next step.
No REPLACE EGR valve.
RECONNECT all components.
RESET PCM to completely clear DTCs.
a-
After Repair Procedure
COMPLETE OBD II Drive Mode.
RERUN OBD Test.
01 - 0 1 A -5 4