Exhaust Gas Recirculation
Exhaust Gas Recirculation
Exhaust Gas Recirculation
The amount of exhaust gas reintroduced and the timing of the cycle varies by calibration. Timing and
volume are controlled by the following:
engine rpm
engine vacuum
exhaust system back pressure
engine coolant temperature
air charge temperature
throttle position
The EGR valve (EGR valve) (9D475) is vacuum-actuated. The vacuum hose routing diagram is shown on
the Vehicle Emission Control Information (VECI) decal.
The EGR system is a differential pressure feedback EGR Sensor system. Differential pressure feedback
EGR Sensor is a subsonic closed loop EGR system. The differential pressure feedback EGR system:
monitors EGR flow rate by the pressure drop across the metering orifice located in the EGR tube.
uses a differential pressure feedback EGR sensor as the feedback device.
uses the EGR valve only as a pressure regulator, rather than a flow metering device.
controlled pressure is varied by the valve movement using vacuum output of the EGR vacuum
regulator solenoid (9J459).
allows for a more accurate assessment of EGR flow requirements.
1. The differential pressure feedback EGR sensor and circuit are continuously tested for opens
and shorts. The monitor looks for the Differential Pressure Feedback EGR circuit voltage to
exceed the maximum or minimum allowable limits.
The DTCs associated with this test are DTCs P1400 and P1401.
2. The EGR vacuum regulator solenoid is continuously tested for opens and shorts. The monitor
looks for an EGR Vacuum Regulator circuit voltage that is inconsistent with the EGR Vacuum
Regulator circuit commanded output state.
3. The test for a stuck open EGR valve or EGR flow at idle is continuously performed whenever
at idle (TP sensor indicating closed throttle). The monitor compares the Differential Pressure
Feedback EGR circuit voltage at idle to the Differential Pressure Feedback EGR circuit voltage
stored during key on engine off to determine if EGR flow is present at idle.
4. The differential pressure feedback EGR sensor upstream hose is tested once per drive cycle
for disconnect and plugging. The test is performed with EGR valve closed and during a period
of acceleration. The PCM will momentarily command the EGR valve closed. The monitor looks
for the differential pressure feedback EGR sensor voltage to be inconsistent for a no flow
voltage. A voltage increase or decrease during acceleration while the EGR valve is closed may
indicate a fault with the signal hose during this test.
The DTC associated with this test is DTC P1405.
5. The EGR flow rate test is performed during a steady state when engine speed and load are
moderate and EGR vacuum regulator duty cycle is high. The monitor compares the actual
Differential Pressure Feedback EGR circuit voltage to a desired EGR flow voltage for that state
to determine if EGR flow rate is acceptable or insufficient. This is a system test and may trigger
a DTC for any fault causing the EGR system to fail.
6. DTC P1408 is similar to P0401 but performed during KOER Self-Test conditions.
7. The MIL is activated after one of the above tests fails on two consecutive drive cycles.
The Exhaust Gas Recirculation (EGR) system controls the oxides of nitrogen (NOx) emissions. Small
amounts of exhaust gases are recirculated back into the combustion chamber to mix with the air/fuel
charge. The combustion chamber temperature is reduced, lowering NOx emissions.
The Differential Pressure Feedback EGR system consists of a differential pressure feedback EGR
sensor, EGR vacuum regulator solenoid, EGR valve, orifice tube assembly, powertrain control module
(PCM) and connecting wires and vacuum hoses. Operation of the system is as follows (Figure 80) :
1. The Differential Pressure Feedback EGR system receives signals from the engine coolant
temperature (ECT) sensor, intake air temperature (IAT) sensor, throttle position (TP) sensor,
mass air flow (MAF) sensor and crankshaft position (CKP) sensor to provide information on
engine operating conditions to the PCM. The engine must be warm, stable and running at a
moderate load and rpm before the EGR system is activated. The PCM deactivates EGR during
idle, extended wide open throttle or whenever a failure is detected in an EGR component or
EGR required input.
2. The PCM calculates the desired amount of EGR flow for a given engine condition. It then
determines the desired pressure drop across the metering orifice required to achieve that flow
and outputs the corresponding signal to the EGR vacuum regulator solenoid.
3. The EGR vacuum regulator solenoid receives a variable duty cycle signal (0 to 100%). The
higher the duty cycle the more vacuum the solenoid diverts to the EGR valve.
4. The increase in vacuum acting on the EGR valve diaphragm overcomes the valve spring and
begins to lift the EGR valve pintle off its seat, causing exhaust gas to flow into the intake
manifold.
5. Exhaust gas flowing through the EGR valve must first pass through the EGR metering orifice.
With one side of the orifice exposed to exhaust backpressure and the other to the intake
manifold, a pressure drop is created across the orifice whenever there is EGR flow. When the
EGR valve closes, there is no longer flow across the metering orifice and pressure on both
sides of the orifice is the same. The PCM constantly targets a desired pressure drop across
the metering orifice to achieve the desired EGR flow.
6. The differential pressure feedback EGR sensor measures the actual pressure drop across the
metering orifice and relays a proportional voltage signal (0 to 5 volts) to the PCM. The PCM
uses this feedback signal to correct for any errors in achieving the desired EGR flow.
Figure 81: Differential Pressure Feedback EGR System Operation (Refer to the On-Board Diagnostics II
System Overview for icon definitions.)
Hardware
Differential Pressure Feedback EGR Sensor
The differential pressure feedback EGR sensor (Figure 81) is a ceramic, capacitive-type pressure
transducer that monitors the differential pressure across a metering orifice located in the orifice tube
assembly. The differential pressure feedback sensor receives this signal through two hoses referred to as
the downstream pressure hose (REF SIGNAL) and upstream pressure hose (HI SIGNAL). The HI and
REF hose connections are marked on the aluminum differential pressure feedback EGR sensor housing
for identification (note that the HI signal uses a larger diameter hose). The differential pressure feedback
EGR sensor outputs a voltage proportional to the pressure drop across the metering orifice and supplies
it to the PCM as EGR flow rate feedback.
The EGR valve (Figure 83) in the Differential Pressure Feedback EGR system is a conventional, vacuum-
actuated EGR valve. The valve increases or decreases the flow of exhaust gas recirculation. As vacuum
applied to the EGR valve diaphragm overcomes the spring force, the valve begins to open. As the
vacuum signal weakens, at 5.4 kPa (1.6 in-Hg) or less, the spring force closes the valve. The EGR valve
is fully open at about 15 kPa (4.5 in-Hg).
Since EGR flow requirement varies greatly, providing service specifications on flow rate is impractical.
The on-board diagnostic system monitors the EGR valve function and triggers a Diagnostic Trouble Code
if the test criteria is not met. The EGR valve flow rate is not measured directly as part of the field
diagnostic procedures.
The orifice tube assembly (Figure 84) is a section of tubing connecting the exhaust system to the intake
manifold. The assembly provides the flow path for the EGR to the intake manifold and also contains the
metering orifice and two pressure pick-up tubes. The internal metering orifice creates a measurable
pressure drop across it as the EGR valve opens and closes. This pressure differential across the orifice is
picked up by the differential pressure feedback EGR sensor which provides feedback to the PCM.
Figure 85: Orifice Tube Assembly
2. Check EGR vacuum regulator solenoid resistance. Reading must be within 30-36 ohms.
3. Connect vacuum pump to lower port. Block off the upper port and apply vacuum. Check if EGR
vacuum regulator solenoid holds vacuum.
4. If resistance reading is out of specification or if EGR vacuum regulator solenoid holds vacuum,
replace EGR vacuum regulator solenoid .
P0402 - EGR The EGR system is monitored for EGR valve stuck A DPFEGR PID reading
Flow undesired EGR flow during idle. open that is greater at idle than
Excessive The EGR monitor looks at the DPF Plugged EGR during key ON and engine
Detected EGR signal at idle and compares it vacuum OFF by 0.5 volt or a rough
to the stored signal measured regulator engine idle, may indicate
during key ON and engine OFF. solenoid vent a hard fault.
The test fails when the signal at Plugged EGR
idle is greater than at key ON tube
engine OFF by a calibrated Slow responding
amount. DPF EGR
sensor
Damaged DPF
EGR sensor
Improper
vacuum hose
connection
Plugged vacuum
hoses
EGRVR circuit
shorted to
ground
Damaged EGR
vacuum
regulator
solenoid
Damaged PCM
Note: If any DTC other than DTC P1406 is output, record DTC and refer to Diagnostic Trouble
Code Charts in Section 4 after completing this Pinpoint Test.
Disconnect vacuum hose at EGR valve and connect hose to a vacuum gauge.
Note: Since the EGR vacuum hose is disconnected, ignore DTCs during this KOER Self-Test.
Run Key On Engine Running (KOER) Self-Test while monitoring gauge. Approximately 30
seconds into test, EGR flow will be requested for a few seconds. The vacuum at this time
should increase above 5.4 kPa (1.6 in-Hg) to open the valve.
Does the vacuum increase to 10 kPa (3.0 in-Hg) or greater at any time during KOER Self-Test?
Yes No
The vacuum indicated is sufficient to open the
EGR valve. Fault is unlikely to be in EGR The vacuum indicated is insufficient to open the
vacuum control system. KEY OFF. GO to HE73 EGR valve. KEY OFF. GO to HE80 .
.
Visually inspect both pressure hoses for reversed connection at D.P.F. EGR sensor or at orifice
tube assembly.
Inspect both hoses for improper routing. Hoses should not be pinched or have dips where water
could settle or freeze.
Inspect both hoses for leaks and blockage.
Inspect D.P.F. EGR sensor and orifice tube assembly for blockage or damage at the pickup
tubes.
Is a fault detected?
Yes No
REPAIR pressure hoses as necessary. GO to HE74 .
HE74 CHECK D.P.F. EGR SENSOR OUTPUT BY APPLYING VACUUM WITH HAND
PUMP
Does the DPFEGR PID voltage indicate a fault in the D.P.F. EGR sensor?
Yes No
REPLACE D.P.F. EGR sensor. RECONNECT pressure hoses. GO to HE76 .
HE76 CHECK EGR VALVE FUNCTION BY APPLYING VACUUM WITH HAND PUMP
Disconnect vacuum hose at EGR valve and plug hose.
Connect a hand vacuum pump to EGR valve.
Start engine and bring to idle.
Access DPFEGR and RPM PIDs.
Slowly apply 27 to 34 kPa (8 to 10 in-Hg) of vacuum to the EGR valve and hold it for 10 seconds.
If engine wants to stall, increase rpm with throttle to maintain a minimum of 1000 rpm.
Look for the following:
EGR valve starts opening at about 5.4 kPa (1.6 in-Hg) vacuum indicated by increasing
DPFEGR PID voltage.
DPFEGR PID voltage increasing until EGR valve is fully open. DPFEGR PID must read
2.5 volts minimum with full vacuum applied.
DPFEGR PID voltage steady when vacuum is held. If voltage drops within a few
seconds, the EGR valve or vacuum source can be leaking.
Does the DPFEGR PID voltage indicate that the EGR valve is operating as described in this test?
Yes No
REMOVE and INSPECT the EGR valve for
signs of contamination, unusual wear, carbon
deposits, binding, leaking diaphragm and other
GO to HE85 . damage. If EGR valve is OK, look for an
obstructed EGR port in the intake manifold or
plugged orifice tube assembly. REPAIR as
necessary.
HE80 CHECK VACUUM SOURCE AND VACUUM HOSES TO AND FROM EGR
VACUUM REGULATOR SOLENOID
Inspect vacuum lines between vacuum source and EGR vacuum regulator solenoid and between
EGR vacuum regulator solenoid and EGR valve for leaks, kinks, disconnects, blockage,
routing or any damage.
Disconnect vacuum hoses at EGR vacuum regulator solenoid.
Connect EGR vacuum regulator solenoid vacuum source hose to a vacuum gauge.
With engine warm and at idle, take vacuum gauge reading.
Is the vacuum gauge reading a minimum of 51 kPa (15 in-Hg) at idle and vacuum lines OK?
Yes No
KEY OFF. GO to HE81 . ISOLATE fault and REPAIR as necessary.
Is EGR vacuum regulator solenoid VPWR voltage greater than 10.5 volts?
Yes No
KEY OFF. GO to HE82 . REPAIR open circuit.
Note: Refer to the PCM connector pin numbers in the beginning of this pinpoint test.
Disconnect PCM.
Key on, engine off.
Measure voltage between EGRVR circuit at the PCM harness connector and battery negative
post.
Measure resistance of EGRVR circuit between PCM harness connector pin and EGR vacuum
regulator solenoid harness connector.
Disconnect vacuum hose at the EGR valve and connect to a vacuum gauge.
Key on, engine running.
With engine at idle, jumper PCM EGRVR circuit to chassis ground.
Is vacuum gauge reading 13.5 kPa (4.0 in-Hg) or greater?
Yes No
REPLACE PCM (refer to Section 2 , Flash
REPLACE EGR vacuum regulator solenoid.
EEPROM).