Mercury MerCruiser MIE 7.4L MPI - Page 707

SERVICE MANUAL NUMBER 23TROUBLE CODE DIAGNOSTICS - 454/502 MAG MPI & 8.2L MPI
Page 5F-10 90-861326--1 MARCH 1999
Code 23 (2 of 2): Intake Air Temperature (IAT) Sensor Circuit (Non-Scan)
STEP ACTION VALUE YES NO
PROCEED TO
1
Was the “On-Board Diagnostic” (OBD) System
Check Performed?
– Step 2
Go to
OBD
System
Check
1. Disconnect IAT sensor.
Greater
Than 4
Ste
p
3
–
2
2. Ignition ON, Engine OFF.
Than
4
Volts
Ste
3
–
2
3. Using a DVOM, check voltage between
IAT sensor harness terminals.
Less
Than 4
Volts
Step 5 –
3
Check resistance across IAT sensor terminals.
It should be less than 25,000 Ohms, refer to
table for approximate temperature to resis-
tance values.
Is it Less Than 25,000 Ohms?
– Step 4 Step 8
4
Check for signal circuit shorted to voltage. If
not shorted to voltage, code 23 is intermittent.
– – –
5
Check for voltage between harness connector
Greater
Than 4
Volts
Step 6 –
5
g
signal circuit and ground.
Less
Than 4
Volts
Step 7 –
6
Faulty sensor ground circuit, faulty connec-
tions, or faulty ECM.
– – –
7
Open signal circuit, faulty connection, or faulty
ECM.
– – –
8 Replace sensor. – – –
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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