SERVICE MANUAL NUMBER 23
TROUBLE CODE DIAGNOSTICS - 7.4L MPI
Code 23 (2 of 3): Intake Air Temperature (IAT) Sensor Circuit (Non-Scan) Low
Temperature Indicated
TEST DESCRIPTION:
Number(s) below refer to step number(s) on the diagnostic table.
STEP4. Check the harness terminals thoroughly for loose connections. If the resistance
of the IAT sensor is monitored, the resistance should steadily decrease as the intake air
warms up. The resistance reading should stabilize when the engine reaches normal op-
erating temperature.
STEP 2. This step checks if there is a problem with the ECM and wiring or if the problem
is the IAT sensor.
STEP 3. This step will isolate the problem to CKT 472 (5 volt reference) or to CKT 813
(sensor ground).
STEP
ACTION
VALUE
YES
NO
PROCEED TO
Go to
Was the “On-Board Diagnostic” (OBD) System
Check Performed?
OBD
System
Check
1
2
–
Step 2
1. Ignition “OFF.”
2.
3.
4.
Disconnect IAT sensor harness terminals.
Ignition “ON,” engine “OFF.”
Connect DVOM across the sensor harness
terminals.
Is voltage above the specified value?
4 Volts
Step 4
Step 6
Step 3
1.
terminal “B” CKT 472 (5 volt reference).
Connect positive (+) DVOM lead to harness
3
2.
Connect negative (–) DVOM lead to a
known good ground.
Is voltage above the specified value?
4 Volts
–
Step 5
–
Locate and repair intermittent faulty connec-
tions. If OK, replace faulty IAT sensor. Is action
complete?
4
5
Locate and repair open CKT 472. If a problem
is found repair as necessary. Was a problem
found?
–
Verify
Repair
Step 7
–
Locate and repair open ground CKT 813. If a
problem is found, repair as necessary. Was a
problem found?
6
7
–
–
Repair faulty ECM connections or replace
faulty ECM. Is action complete?
90-861326--1
MARCH 1999
Page 5G-15
| Categories | Mercury MerCruiser Manuals |
|---|---|
| Tags | Mercury MerCruiser 454 CID, Mercury MerCruiser 502 CID |
| Model Year | 1998, 1999, 2000, 2001 |
| Download File |
|
| Document File Type | |
| Copyright | Attribution Non-commercial |
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