Acura RL (1996-2004 year). Manual — part 401
Emission Control System
Exhaust Gas Recirculation (EGR) System (cont'd)
The scan tool indicates Diagnostic Trouble Code (DTC) P1491: An insufficient lift of the Exhaust Gas Recirculation
(EGR) valve.
Is DTC P1491 indicated?
YES
Check for vacuum to the EGR
valve:
1. Disconnect the No. 11 hose from
the EGR valve.
2. Connect vacuum pump/gauge
to the hose.
3. Start the engine and let it idle.
Is there any vacuum?
YES
Check for a malfunction in the
EGR valve vacuum control
solenoid valve:
1. Disconnect the control box 4P
connector.
2. Recheck the No. 11 hose for
vacuum.
Intermittent failure, system is OK
at this time. Check for poor con-
nections or loose wires at C251,
C254 (located at left shock tower),
C107 (EGR valve) and PCM.
NO
VACUUM PUMP/GAUGE, 0 - 30 in.Hg
No. 11 VACUUM
HOSE
EGR
VALVE
NO
Problem verification:
1. Do the PCM Reset Procedure.
2. Connect the SCS service con-
nector.
3. Start the engine. Hold the
engine at 3,000 rpm with no
load (in Park or neutral) until
the radiator fan comes on.
4. Drive the vehicle on the road for
approx. 10 minutes. Try to keep
the engine speed in the 1,700 -
2,500 rpm range.
The MIL has been reported on.
DTC P1491 is stored.
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Is there any vacuum?
NO
Check for a short in the wire (ES
line):
1. Turn the ignition switch OFF.
2. Disconnect the PCM connec-
tor A (26P).
3. Check for continuity between
body ground and the control
box 4P connector terminal No. 2.
Is there continuity?
NO
Substitute a known-good PCM
and recheck (see page
for
immobilizer information). If symp-
tom/indication goes away, re-
place the original PCM.
Check for a malfunction in the
EGR valve:
1. Move the vacuum pump/gauge
to the EGR valve.
2. With the engine at idle, apply
26.7 kPa (200 mmHg, 8.0 in.Hg)
of vacuum to the EGR valve.
Does the engine stall or run
rough and does the EGR valve
hold vacuum?
YES
Check for an open in the wire
(VCC2 line):
1. Turn the ignition switch OFF.
2. Disconnect the EGR valve
position sensor 3P connector.
3. Turn the ignition switch ON (II).
4. Measure voltage between the
EGR valve position sensor 3P
connector terminals No. 1 and
No. 3.
Is there approx. 5 V?
NO
Check vacuum hose routing of
the entire EGR system. If hose
routing is OK, replace the EGR
valve vacuum control solenoid
valve.
CONTROL BOX 4P CONNECTOR (C257)
Wire side of female terminals
Repair short in the wire between
PCM (A6) and EGR valve vacuum
control solenoid valve.
VACUUM
PUMP/GAUGE,
0 - 30 in.Hg
Replace the EGR valve.
EGR
VALVE
No. 11
VACUUM
HOSE
EGR VALVE POSITION SENSOR CONNECTOR (C107)
Wire side of female terminals
YES
NO
YES
YES
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Emission Control System
Exhaust Gas Recirculation (EGR) System (cont'd)
PCM CONNECTOR D (22P)
Check for an open in the wire
(VCC2 line):
Measure voltage between the
PCM connector terminals D21
and D22.
Is there approx. 5 V?
NO
Substitute a known-good PCM
and recheck (see page
for
immobilizer information). If
symptom/indication goes away,
replace the original PCM.
Repair open in the wire between
the EGR valve and PCM (D21).
Check for an open or short in the
EGR valve position sensor:
1. Turn the ignition switch OFF.
2. At the sensor side, measure
resistance between the EGR
valve position sensor 3P connec-
tor terminals No. 1 and No. 2.
Is there continuity or resis-
tance of 100 k or higher?
NO
Check for an open or short in the
EGR valve position sensor.
Measure resistance between the
EGR valve position sensor 3P con-
nector terminals No. 2 and No. 3.
Is there 100 Kfi or higher?
YES
Check for an open or short in the
wire (EGRL line):
1. Reconnect the EGR valve
position sensor 3P connector.
2. Turn the ignition switch ON (II).
3. Measure voltage between the
PCM connector terminals D17
and D22.
Is there approx. 1.2 V?
EGR VALVE POSITION SENSOR CONNECTOR
Replace the EGR valve.
Terminal side of male terminal
Replace the EGR valve.
PCM CONNECTOR D (22P)
YES
Wire side of female terminals
NO
NO
YES
YES
Wire side of female terminals
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PCM CONNECTOR D (22P)
Check for a short in the wire
(EGRL line):
Check for continuity between
PCM connector terminal D17 and
the body ground.
Is there continuity?
Repair open in the wire between
the EGR valve and the PCM (D17).
YES
Repair short in the wire between
the EGR valve and PCM (D17).
Check for an open in the wire (IG1
line):
1. Turn the ignition switch OFF.
2. Disconnect the control box
connector.
3. Turn the ignition switch ON (II).
4. Measure voltage between body
ground and the control box
connector terminal No. 1.
Wire side of female terminals
CONTROL BOX 4P CONNECTOR (C257)
Wire side of female terminals
Is there battery voltage?
YES
Check the vacuum routing:
1. Reconnect the vacuum pump/
gauge to the No. 11 hose.
2. Start the engine and let it idle.
3. At the control box side, con-
nect the battery positive ter-
minal to the EGR valve vacu-
um control solenoid valve
connector terminal No. 1.
4. While watching the vacuum
gauge, connect the battery neg-
ative terminal to the EGR valve
vacuum control solenoid
valve connector terminal No. 2.
Repair open in the wire between
the EGR valve vacuum control
solenoid valve and No. 20 ECU
(PCM) (20 A) fuse in the under-
dash fuse/relay box.
CONTROL BOX 4P
CONNECTOR
Is there approx. 26.7 kPa
(200 mmHg, 8.0 in.Hg) of vacu-
um within 1 second?
Terminal side
of male terminals
NO
YES
Check the vacuum hoses:
1. Turn the ignition switch OFF.
2. Inspect the No. 11 and No. 3
hoses for leaks, restrictions or
misrouting.
Are the hoses OK?
Correct as necessary.
YES
NO
NO
Replace the EGR valve vacuum
control solenoid valve.
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