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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