Mercury MerCruiser MCM 454 Mag MPI Service Manual page 763

TROUBLE CODE DIAGNOSTICS - 7.4L MPI
Code 25 (3 of 3): Intake Air Temperature (IAT) Sensor Circuit (Non-Scan) High
Temperature Indicated
STEP
1
2
3
4
5
INTAKE AIR TEMPERATURE SENSOR CHART
Index
Page 5G-18
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ACTION
Was the "On-Board Diagnostic" (OBD) System
Check Performed?
1. Ignition "OFF."
2. Disconnect IAT sensor harness terminals.
3. Ignition "ON," engine "OFF."
4. Connect DVOM across the sensor harness
terminals.
Is voltage above the specified value?
Locate and repair intermittent faulty connec-
tions. If OK, replace faulty IAT sensor.
Locate and repair short to ground in CKT 472.
If a problem is found, repair as necessary. Was
a problem found?
Repair faulty ECM connections or replace
faulty ECM. Is action complete?
Temperature - to - Resistance Values (Approximate)
F
210
160
100
70
40
20
0
-40
VALUE
–
4 Volts
–
–
–
IAT Sensor
C
100
70
38
20
4
-7
-18
-40
SERVICE MANUAL NUMBER 23
YES NO
PROCEED TO
Go to
OBD
Step 2
System
Check
Step 3 Step 4
–
Verify
Step 5
Repair
–
OHMS
185
450
1,800
3,400
7,500
13,500
25,000
100,700
90-861326--1 MARCH 1999