SERVICE MANUAL NUMBER 23
TROUBLE CODE DIAGNOSTICS - 7.4L MPI
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
Go to
Was the “On-Board Diagnostic” (OBD) System
Check Performed?
OBD
System
Check
1
2
–
Step 2
Ignition “ON.”
2
66°F
Does the scan tool display a temperature
greater than the specified value?
(130
°C)
Step 3
Step 6
Step 4
3
1. Ignition “OFF.”
2.
3.
Disconnect IAT harness connector.
Ignition “ON,” engine “OFF.”
-
22°F
(-30
°C)
Does scan tool display a temperature be-
low the specified value?
Step 5
–
Trouble code 25 is intermittent. Locate and re-
pair intermittent faulty connections. Refer to
“Diagnostic Aids”.
4
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
7
Repair faulty IAT sensor. Is action complete?
–
–
–
–
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
100
70
38
20
4
-7
-18
-40
185
450
1,800
3,400
7,500
13,500
25,000
100,700
0
-40
90-861326--1
MARCH 1999
Page 5G-51
| 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 |
(1 votes, average: 5 out of 5)
Marine readers have rated Mercury MerCruiser GM V8 GM V8 454 CID 7.4L and 502 cid 8.2L Marine Engines Service Manual Number 23 5.0 out of 5.0 based on 1 product reviews. Just need the manual. Wrote review. Can't technically review what I haven't seen yet...