DL - Testing Notes

DESCRIPTION
The Pressure Feedback Electronic (PFE) EGR system consists of a pressure sensor (PFE sensor), Electronic Vacuum Regulator (EVR) solenoid, and a vacuum actuated EGR valve. The Differential Pressure Feedback Electronic (DPFE) EGR system uses a differential pressure sensor (DPFE sensor) which has two pressure inlets rather than one as in the PFE system.

In both systems, the EVR solenoid regulates a vacuum signal to the EGR valve in response to a duty cycle signal from the Powertrain Control Module (PCM). The EVR solenoid will vent some of the source vacuum and transmit the remaining vacuum to the EGR valve in response to the level of the duty cycle. The higher the duty cycle, the more vacuum is transmitted to the EGR valve. Due to the design of the EVR solenoid, the available vacuum at the EGR valve never reaches the source vacuum level.

EGR Flow:

EGR flow rate is determined by monitoring the pressure across a fixed metering orifice as exhaust gasses pass through it. The DPFE system monitors this flow across the orifice by supplying the DPFE sensor with a pressure signal before the orifice (upstream pressure) and a pressure signal after the orifice (downstream pressure). The DPFE sensor then evaluates these two pressure inputs and determines the pressure difference across the orifice. This pressure difference translates to a specific EGR flow which the DPFE sensor signals the PCM by an analog voltage signal. This signal to the PCM increases linearly as the differential pressure increases. The PFE system, unlike the DPFE system, has only one pressure signal input (downstream) and must rely on the PCM to indirectly infer the upstream exhaust pressure in order to determine the EGR flow rate. The PFE sensor transmits an analog voltage signal which decreases linearly as EGR flow increases.

With the feedback signal that either the PFE or DPFE sensors provide, the PCM can then optimize the EGR flow rate by varying the EVR duty cycle.


NOTE
You should enter this Pinpoint Test only when you have been directed here from Diagnostic Routines.

REMEMBER
To prevent the replacement of good components, be aware that the following non-Electronic Engine Controls (EEC) areas may be at fault:

- Damaged EGR valve

- Damaged vacuum reservoir

- Restricted exhaust

This Pinpoint Test is intended to diagnose only the following:

- Harness circuits: VREF, DPFE, SIG RTN, EVR, VPWR

- DPFE sensor

- EGR valve assembly

- PFE sensor

- Vacuum lines (EVR, PFE/DPFE)

- EVR solenoid

- Powertrain Control Module