881731 Mercruiser SENSOR, Manifold Air Pressure

Illustration 1 g01214470
Schematic for digital sensor supply
Test Step 1. INSPECT THE ELECTRICAL CONNECTORS AND THE WIRING
Remove electrical power from the engine ECM.
Thoroughly inspect the J1/P1 ECM connector and the connector for the throttle position sensor. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
Illustration 2 g01167488
Location of the J1/P1 ECM connectors (typical engine view)
(1) J1/P1 ECM connectors
Illustration 3 g01213916
Location of the engine interface connectors (typical left side engine view)
(2) engine interface connectors
Thoroughly inspect connectors (1) and (2). Also, thoroughly inspect the connector for the digital sensor. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
Illustration 4 g01214474
Terminal locations at the P1 ECM connector for the digital sensor supply
(P1-4) 8 VDC supply
(P1-5) Digital return
(P1-66) Throttle position
Illustration 5 g01214475
Terminal locations at the engine interface connector for the digital sensor supply
(Terminal 33) 8 VDC supply
(Terminal 34) Digital return
(Terminal 35) Throttle position
Illustration 6 g01159881
Terminal locations at the sensor connector for the digital sensor supply
(Terminal A) 8 VDC supply
(Terminal B) Digital return
(Terminal C) Throttle position
Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector and the connector for the throttle position sensor.
Check the allen head screw from each ECM connector for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct torque value.
Check the harness and the wiring for abrasion and for pinch points. Expected Result:All of the connectors, pins and sockets are completely coupled and/or inserted and the harness and wiring are free of corrosion, of abrasion and of pinch points.Results:
OK - The harness and connectors appear to be OK. Proceed to Test Step 2.
Not OK - The connectors and/or wiring are not OK.Repair: Repair the connectors or wiring and/or replace the connectors or wiring. Ensure that all of the seals are properly in place and ensure that the connectors are completely coupled.STOPTest Step 2. CHECK FOR ACTIVE DIAGNOSTIC CODES
Connect Caterpillar Electronic Technician (ET) to the service tool connector.
Restore electrical power to the engine ECM.
Monitor the active diagnostic code screen on Cat ET. Check and record any active diagnostic codes. Note: Wait at least 30 seconds in order for the diagnostic codes to become active.Expected Result:There are no active diagnostic codes.Results:
OK - No diagnostic code for the digital supply is active. A problem is suspected with a sensor output signal. In order to verify that the sensor is receiving the correct supply voltage, proceed to Test Step 3.
Not OK - A 41-03 diagnostic code is active. The ECM is detecting a short to the +Battery in the wiring for the digital supply. Proceed to Test Step 3.
Not OK - A 41-04 diagnostic code is active. The ECM is detecting a short to ground in the wiring for the digital supply. Proceed to Test Step 4.Test Step 3. CHECK THE SUPPLY VOLTAGE AT THE SENSOR CONNECTOR
Remove electrical power from the engine ECM.
Disconnect the throttle position sensor at the sensor connector.
Restore electrical power to the engine ECM.
Measure the voltage between terminals A (8 V digital supply) and terminal B (digital return) at the sensor connector. Expected Result:The voltage is 8.0 0.5 VDC.Results:
OK - The voltage is 8.0 0.5 VDC. The voltage is correct.Repair: Restore all wires to the original configuration. Clear all diagnostic codes. The problem seems to be resolved. There may be an intermittent problem in the circuit. If an intermittent problem is suspected, refer to Troubleshooting, "Electrical Connectors - Inspect" for details.STOP
Not OK - The voltage is not 8.0 0.5 VDC. The voltage is incorrect at the sensor connector. Proceed to Test Step 5.Test Step 4. DISCONNECT THE SENSOR CONNECTOR AND CHECK FOR ACTIVE DIAGNOSTIC CODES
Remove electrical power from the engine ECM.
Ensure that the throttle position sensor is disconnected at the sensor connector.
Restore electrical power to the engine ECM.
Use Cat ET to check an active 41-04 diagnostic code. Note: Wait for 30 seconds after the sensor is disconnected. Check for an active diagnostic code on Cat ET.Expected Result:The 41-04 diagnostic code deactivates while the sensor is disconnected from the circuit.Results:
OK - The 41-04 diagnostic code deactivates while the sensor is disconnected.Repair: The harness and the ECM are OK. There is a problem with the sensor. Replace the sensor. Ensure that the code does not return with the new sensor prior to installing the new sensor. Verify that the repair eliminates the problem.STOP
Not OK - The 41-04 diagnostic code remains active when the sensor is disconnected from the circuit. Leave the sensor disconnected. Proceed to Test Step 5.Test Step 5. CHECK THE +8 V SUPPLY WIRE AT THE ECM CONNECTOR FOR A SHORT IN THE HARNESS
Remove electrical power from the engine ECM.
Disconnect the J1/P1 ECM connectors.
Ensure that the throttle position sensor is disconnected at the sensor connector. Note: Wiggle the harness during the following measurements in order to reveal any intermittent short condition.
Measure the resistance between P1-4 (+8 V digital supply) and every terminal on the P1 ECM connector.
Measure the resistance between P1-4 (+8 V digital supply) and engine ground. Expected Result:Each resistance measurement indicates that an open circuit condition exists.Results:
OK - All measurements indicate an open circuit. Leave the connector disconnected. There is not a short circuit