MerCruiser 305 CID (5.0L) Service Manual page 694

SERVICE MANUAL NUMBER 24
Code 25 (2 of 2): Engine Coolant Temperature (IAT) Sensor Circuit
Step
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Index
90-861327--1 OCTOBER 1999
Was the "On-Board Diagnostic" (OBD) System Check
Performed?
Are you using a Scan Tool?
Ignition ON.
Does the scan tool display a temperature greater
than 266°F (130°C)?
a. Ignition OFF.
b. Disconnect IAT harness connector.
c. Ignition ON, engine OFF.
Does scan tool display a temperature below -22°F
(-30°C)?
Trouble code 25 is intermittent. Locate and repair inter-
mittent faulty connections. Refer to "Diagnostic Aids."
Locate and repair short to ground in CKT 472. If a prob-
lem is found, repair as necessary.
Was a problem found?
a. Ignition OFF.
b. Disconnect IAT sensor harness terminals.
c. Ignition ON, engine OFF.
d. Connect DVOM across the sensor harness terminals.
Is voltage above 4 volts?
Locate and repair intermittent faulty connections or re-
place faulty IAT sensor.
Locate and repair short to ground in CKT 472.
Repair faulty ECM connections.
Action
DIAGNOSTICS
Yes No
PROCEED TO
Step 2. OBD
Step 3. Step 7.
Step 4. Step 5.
Step 8. Step 6.
–
Verify
Repair
Step 10.
Step 8. Step 9.
–
Verify
Step 10.
Repair
–
Page 5G-67