Mercury MerCruiser MCM 7.4L MPI User Manual

TROUBLE CODE DIAGNOSTICS - 7.4L MPI
SERVICE MANUAL NUMBER 23
90-861326--1 MARCH 1999 Page 5G-51
Code 25 (2 of 2): Engine Coolant Temperature (IAT) Sensor Circuit (Scan) High
Temperature Indicated
TEST DESCRIPTION:
Number(s) below refer to step number(s) on the diagnostic table.
Step 2. DTC 25 will set if signal voltage indicates a coolant temperature above 266° F
(130° C).
Step 3. This test simulates a DTC 23. If the ECM recognizes the high voltage signal and
displays a low temperature, the ECM and wiring are OK.
STEP
ACTION VALUE YES NO
PROCEED TO
1
Was the “On-Board Diagnostic” (OBD) System
Check Performed?
– Step 2
Go to
OBD
System
Check
2 Ignition “ON.”
266
°
F
Does the scan tool display a temperature
greater than the specified value?
266 F
(130°C)
Step 3 Step 4
3 1. Ignition “OFF.”
2. Disconnect IAT harness connector.
-
22
°
F
3. Ignition “ON,” engine “OFF.”
-
22 F
(-30°C)
Does scan tool display a temperature be-
low the specified value?
( )
Step 6 Step 5
4
Trouble code 25 is intermittent. Locate and re-
pair intermittent faulty connections. Refer to
“Diagnostic Aids”.
– –
5
Locate and repair short to ground in CKT 472.
If a problem is found, repair as necessary.
Was
a problem found?
–
Verify
Repair
Step 7
6 Repair faulty IAT sensor. Is action complete? – –
7
Repair faulty ECM connections or replace
faulty ECM.
Is action complete?
– –
INTAKE AIR TEMPERATURE SENSOR CHART
IAT Sensor
Temperature - to - Resistance Values (Approximate)
°F °C OHMS
210
160
100
70
40
20
0
-40
100
70
38
20
4
-7
-18
-40
185
450
1,800
3,400
7,500
13,500
25,000
100,700
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Index

Mercury MerCruiser MCM 7.4L MPI Specifications

General

Brand	Mercury
Model	MerCruiser MCM 7.4L MPI
Category	Engine
Language	English