Tricky diagnosis... need help to pinpoint the issue.
2008 Explorer, 120K miles, V6 4.0L

Throwing DTC P0402 code.
Mode $06 - OnBoard Monitoring

Component Description Value Minimum Maximum Units Result
$32 - EGR Monitor Bank 2 TID $82 - Manufacturer Defined 32.102 -32.768 32.663 kPa Pass
$32 - EGR Monitor Bank 2 TID $83 - Manufacturer Defined 32.102 -3.633 32.767 kPa Pass
$32 - EGR Monitor Bank 2 TID $84 - Manufacturer Defined 32.103 -32.768 7.971 kPa Fail
$32 - EGR Monitor Bank 2 TID $85 - Manufacturer Defined 0 0 32.767 kPa Pass

The EGR valve is an assembly with DPFE sensor included. Both vacuum lines to the DPFE at idle read 18mmHg & 19 mmHg.

The 2008 ODB Service Manual indicates this for TID $84:
The differential pressure indicated by the DPFE sensor is also checked at idle with zero requested EGR flow
to perform the high flow check. If the differential pressure exceeds a calibratable limit, it indicates a stuck open
EGR valve or debris temporarily lodged under the EGR valve seat (P0402).

Replaced EGR assembly: no help... P0402 comes back after the required drive cycles are reached when resetting DTCs.

Other possibilities?
Could the new part be bad or incompatible? (aftermarket not Motorcraft).
Electric issue or wiring? PCM issue?

Please help!

 

Which engine?

Have you followed the correct Pinpoint in the PCED?

 

Engine: V6 4.0L
What is PCED?

The 2008 OSM describes the following:

DPFE EGR Stuck open Check Operation:
DTCs P0402
Monitor execution once per driving cycle
Monitor Sequence Done after electrical tests
Sensors OK: CPS, ECT, IAT, MAF, TP <-- not sure about these other sensors
Monitoring Duration 10 seconds to register a malfunction

The EGR assembly only has signals for the EVR, MAF, & DPFE.

 

I'm familiar with the OSM. It is not a diagnostics manual.

The PCED (Powertrain Control & Emissions Diagnostics) is the manual with the troubleshooting procedures.

 

Search efforts for PCED are spurious at best.
Have a link for a copy that applies to a V6 4.0L 2008yr ?

 

Search eBay for "2008 Ford service DVD"

 

The EGR System Module DPFE has 2 vacuum line ports.
I tried applying 10mmHg to each but only one can hold a vacuum. The PC/ED only says to check the "downstream differential pressure feedback EGR sensor port".
Pinpoint HH13 passes all voltages w/ the 10mmHg on one port.

The other port is the Vacuum Regulator port for pinpoint HH14. Which bleeds to normal atmosphere.

HH15 is covered by a second replacement OEM Motorcraft EGR System Module.
The pinpoint diagnosis ends with HH15 for P0402 DTC.

Maybe PCM or a bad signal from the EGR module?
Any experts out there to provide any further guidance?



REFERENCES:

Service Manual:
Exhaust Gas Recirculation (EGR) System Module (ESM)The ESM is an integrated differential pressure feedback EGR system that functions in the same manner as a conventional differential pressure feedback EGR system. The various system components have been integrated into a single component called the ESM. The flange of the valve portion of the ESM bolts directly to the intake manifold with a metal gasket that forms the metering orifice. This arrangement increases system reliability, response time, and system precision. By relocating the EGR orifice from the exhaust to the intake side of the EGR valve, the downstream pressure signal measures manifold absolute pressure (MAP). This MAP signal is used for EGR correction and inferred barometric pressure (BARO) at key on. The system provides the powertrain control module (PCM) with a differential pressure feedback EGR signal, identical to a traditional differential pressure feedback EGR system.

PC/ED instruction:

HH13 SIMULATE THE DIFFERENTIAL PRESSURE FEEDBACK EGR SENSOR SIGNAL WITH A VACUUM PUMP

• Disconnect the downstream differential pressure feedback EGR sensor port hose at the ESM.
• Verify the hose and port are clear and free of obstructions.
• Connect a vacuum pump to the downstream differential pressure feedback EGR sensor port.
• Key ON, engine OFF.
• Access the PCM and monitor the DPFEGR PID.
• Apply 27 - 30 kPa (8 - 9 in-Hg) vacuum to the differential pressure feedback EGR sensor and hold for 10 seconds.
• Quickly release the vacuum.
  • The DPFEGR PID voltage must be between 0.25 and 1.3 volts with the key ON and no vacuum applied.
  • The DPFEGR PID voltage must increase to greater than 4 volts with the vacuum applied.
  • The DPFEGR PID must drop to less than 1.5 volts in less than 3 seconds when the vacuum is released.

HH14 INSPECT THE EGR VACUUM REGULATOR SOLENOID VENT FOR BLOCKAGE

Note: When the EGR valve is closed, the EGR vacuum regulator solenoid vacuum is vented through the solenoid vent to the atmosphere. A plugged EGR vacuum regulator solenoid vent does not allow EGR vacuum to vent to the atmosphere.

• EGR vacuum regulator vacuum hoses disconnected.
• Connect a hand vacuum pump to the EGR vacuum regulator source port.
• Apply 34 to 51 kPa (10 to 15 in-Hg) vacuum.

HH15 CHECK THE EGR VALVE FOR CARBON BUILD-UP

• Remove the ESM.
• Visually inspect the EGR valve and valve seat for correct seating, carbon build-up and debris.

 

PROBLEM SOLVED.

Very subtle insulation cracks in the wiring harness to the EGR module. Subtle because it was just peeking past the corrugated tubing and tape. Removing the tape and tubing carefully revealed several exposed wires that appeared as if they could have been shorting together. This would explain why some signals worked and others had a strange reading from the scan tool monitor.
Probably should have ohmed out all combinations at the connector end (6 pins = 15 combinations of 2 wires).

1. New OEM EGR valve
2. Repaired wire harness
3. Drive cycle completion for the PCM reset

No codes!
Ready for emission testing.