EGR System - MIL ON/DTC's Set

Article No.
99-10-3

06/01/99

ENGINE - 3.0L - EGR SYSTEMS DIAGNOSIS -
SERVICE TIPS

LIGHT TRUCK:
1993-1998 VILLAGER

ISSUE
The "Check Engine" warning lamp may illuminate and Diagnostic Trouble Codes (DTCs) 32, 35 (1993-1995 vehicles), P0400, P0402, P1400, P1401, P1402 or Malfunction Indicator Lamp (MIL) DTC 0302, 0305, 0306, 0514, 1005 (1996-1998 vehicles) may be stored indicating a malfunction in the Exhaust Gas Recirculation (EGR) system. This may be caused by failure of any of the several components that make up the EGR system.

ACTION
Refer to the following EGR System Description and perform the accompanying pinpoint test steps to identify the failed component.

EGR SYSTEM DESCRIPTION





EGR System Operation

The EGR system recirculates a portion of the exhaust gases back into the intake manifold under average vehicle driving conditions to reduce combustion temperatures and exhaust gas Nitrous Oxide (NOx) emissions. The amount of exhaust gas recirculated varies according to the operating conditions and will be cut completely during:

^ Engine starting

^ Cold engine operation (less than 75°C/167°F)

^ Excessively hot engine operation

^ Engine idling

^ Wide open throttle

^ Mass Air Flow (MAF) sensor failure

The EGR system on the Villager uses the Exhaust Gas Recirculation Control (EGRC) solenoid to provide vacuum to both the EGR valve and the EVAP canister when commanded by the Powertrain Control Module (PCM). If the exhaust backpressure is sufficient to close the EGR Backpressure Transducer (BPT) valve, vacuum is sent to the EGR valve which allows exhaust gas to flow into the intake manifold. If the exhaust backpressure is not sufficient, the EGR BPT will remain open and the vacuum from the EGRC solenoid is vented to the atmosphere.








The PCM uses a temperature sensor to monitor EGR system operation. The EGR temperature sensor is a thermistor located in the EGR passageway. When hot exhaust gas is recirculated into the engine, the sensor temperature increases which causes its resistance to decrease. The decreased resistance causes the voltage signal at the PCM to also decrease indicating EGR flow. For OBDII vehicles, if the EGR temperature sensor does not detect EGR flow when commanded by the PCM after 2 consecutive trips, the MIL will be illuminated and a DTC will be stored. The MIL will be turned off after 3 consecutive trips are completed with no faults detected. The DTC, however, will remain stored in the PCM memory until 80 trips have been completed without the same malfunction detected in the system. Refer to Figure 1 for 1993-1997 vehicles, and Figure 2 for 1998 vehicles.

NOTE
THE EVAPORATIVE EMISSIONS (EVAP) SYSTEM ON 1998 CALIFORNIA EMISSION VEHICLES IS NOT PART OF THE EGR SYSTEM.

EGR Backpressure Transducer (BPT)





The EGR BPT is used to control EGR. The EGR valve is operated by either ported (1993-1997 vehicles) or manifold (1998 vehicles) vacuum, but the vacuum will normally be vented off at the EGR BPT. As engine rpm increases, exhaust backpressure increases and pushes on the diaphragm in the EGR BPT and closes the vacuum vent. Refer to Figure 3.

EGR Control (EGRC) Solenoid








The EGR Control (EGRC) solenoid controls vacuum to both the EGR and EVAP systems (the EVAP system on California emission vehicles is separate) and is operated by the PCM. The PCM grounds the circuit from the EGRC to activate the solenoid. Refer to the EGR System Operation Chart to determine which model years pass or block vacuum to the EGR and EVAP systems when the solenoid is "activated." Refer to Figure 4 for 1993-1997, and Figure 5 for 1998 vehicles.

EGR Temperature Sensor





The EGR temperature sensor is a thermistor-type sensor that monitors the temperature within the EGR passageway. As EGR flow increases, the temperature increases. This causes the sensor resistance and signal voltage at the PCM to decrease. If the EGR temperature sensor signal voltage does not change as the PCM expects on 2 consecutive trips (OBDII vehicles), the MIL will be illuminated and a DTC will be stored. Refer to Figure 6.

EGR Valve





The EGR valve recirculates a portion of the exhaust gas back into the intake manifold to reduce combustion temperature and therefore the amount of NOx exhaust emissions. The amount of exhaust gas recirculated is proportional to the load on the engine. Refer to Figure 7.
































Refer to Figures 8-17 for Pinpoint Tests of the EGR System.





Parts Block

OTHER APPLICABLE ARTICLES: NONE
WARRANTY STATUS: INFORMATION ONLY
OASIS CODES: 698298