Usage:
1. Disconnect plug P11 to Throttle Position Sensor from receptacle J11. The locking ring helps identify P11 from J11. Check the connections for damaged wires or pins and corrosion. Also check that the pins are at the proper height in the connector. Check that the wires and pins are tight in the connectors by pulling (slightly) on each wire of each connector (including the breakout "T").
2. Install 8T8726 Adapter (3-pin breakout "T") between J11 and P11. Twist the locking rings to secure the connections.
3. Connect the voltmeter as shown. Check for the appropriate voltages between the lettered "T" pins as explained in Steps 4 through 6.
4. Check sensor supply voltage.
Pin A (+) to pin B (ground) system voltage should be approximately 12 volts DC with key on (no accessories). Minimum voltage is 11.0 volts DC. While cranking, the voltage should be 8 to 12 volts DC.
Diagnosis - Using the truck wiring schematic, check wires A and B and connections from J11 through the 10A sensor fuse and the truck wiring harness back to the battery terminals for proper voltage.
5. Check for poor power connection.
If the voltage check between pins A and B is less than 11.0 volts with the key on, check the voltage drop from pin B to the negative battery post while cranking. For this test, the common lead (black) should be connected to the negative battery post first. Then place the positive (red) lead into pin B. (Pin B is chassis ground). Voltage should be less than 0.5 volts DC when cranking.
Diagnosis - If the voltage drop is greater than 0.5 volts DC, check wire B and connections (including the battery post connections) from J11 to battery negative. Follow the truck wiring schematic to trace the electrical path from J11 to chassis ground.
6. Check throttle signal.
Pin C (throttle) to pin B (throttle return):
- * Less than 1.0 volt DC with the key on and the foot pedal in the low idle position.* More than 3.5 volts DC with the foot pedal in the high idle position.
Diagnosis - If pin A to pin B voltage is proper and the voltage from pin C to pin B does not vary from low idle to high idle, check J11 pin C and socket connection. Check for broken throttle linkage from foot pedal to throttle position sensor. (Throttle position sensor may need adjustment or replacement. See Electronic Troubleshooting, 3406C (PEEC III) Diesel Truck Engine, Form No. SENR5503, or the Testing and Adjusting section in Systems Operation, Testing and Adjusting, 3406C (PEEC III) Diesel Truck Engine, Form No. SENR5508. The throttle position sensor is a Caterpillar supplied part, but initial adjustment is OEM responsibility.)
NOTE: Diagnostic code 32, Throttle Position Sensor Fault, will be generated if the throttle signal is not received by the ECM for at least one half second. This will limit engine rpm to low idle.
7. Restore connections.
Disconnect breakout "T" and reconnect P11 to J11. Secure the locking ring.
If problem has not been resolved, proceed to the next connector to be tested as shown in the Operational Problem Chart section.
If this is the last connector to be checked for the operational problem being investigated:
- * The problem could lie within the System Configuration Parameters or the Customer Specified Parameters. Check with the 3406C (PEEC III) (7X6400) DDT or the (8T8697) ECAP.
NOTE: Diagnostic Code 56, Check Customer or System Parameters, may limit engine power or may limit engine speed to low idle, depending on the parameter causing the code 56.