Circuit Description
The optical sensor provides a pump cam signal to the powertrain control module (PCM) by counting the pulses from the sensor that monitors slots on the data track disk that is located inside the injection pump. The pump cam is one of the most important PCM inputs for fuel control and timing. This test monitors the number of crankshaft position pulses that have occurred since the last cam pulse. The physical one-to-one correspondence between the pump cam and the crankshaft implies that if more crank pulses than cam pulses are detected, the cam pulses have been missed.
Conditions for Running the DTC
The engine is operating.
Conditions for Setting the DTC
| • | Eight consecutive cam pulses are missing. |
| OR |
| • | An average of eight cam pulses are missing. |
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL) on the first drive trip in which the diagnostic runs and fails. |
| • | The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, this information is stored in the Freeze Frame and/or Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn the MIL off after 3 consecutive trips without a fault condition. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures. |
| • | The scan tool Clear Info function was used. |
Diagnostic Aids
Intermittent DTCs P0251, P0370, and P1216 may be caused by air entering the fuel system when fuel levels are less than 1/8 of a tank while the driver is performing hard acceleration or turning maneuvers. A P0251, P0370, and P1216 may set if the vehicle has run out of fuel. Verify the customer's driving habits to determine if the vehicle has been performing in these manners. If the vehicle has been performing in these conditions, bleed the fuel system of all air and test drive the vehicle.
When the PCM is in backup fuel, fast idle and faulty performance problems will exist.
An intermittent condition may be caused by:
| • | Faulty connections |
| • | Rubbed-through wire insulation |
| • | Broken wire inside the insulation |
Review Freeze Frame and Failure Records. If code P0251 is set at 0 RPM, the code is false and should be ignored.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step determines if this is a hard or intermittent DTC.
-
This step determines if there is a 5-volt reference.
-
This step verifies whether the sensor is sending a signal back to the PCM.
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The PCM supplies 5 volts on the signal circuit. This step determines if that voltage is present, not present, or if too much voltage is present.
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This step determines if the signal circuit is shorted to 5 volt. A normal CAM signal circuit will have 3-5 mA. Any reading over 35 mA indicates a short to 5 volt.
-
This step ensures that the replacement PCM, which utilizes an electrically erasable programmable read-only memory (EEPROM), is programmed when installed.
Step | Action | Values | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
1 |
Important: Before clearing the DTCs, use the scan tool Capture Info to save the Freeze Frame and Failure Records for reference. The data in the control module is deleted once the Clear Info function is used. Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||||||||
2 | Is DTC P0370 set also? | -- | Go to DTC P0370 Timing Reference High Resolution System Performance | |||||||
Does scan tool display the specified value? | 8 | |||||||||
4 | The DTC is intermittent. If no additional DTCs are stored, refer to Diagnostic Aids. If additional DTCs are stored, refer to the applicable DTC tables first. Are any additional DTCs stored? | -- | Go to the applicable DTC table | Go to Diagnostic Aids | ||||||
Is the voltage within the specified range? | 4.8-5.2 V | |||||||||
6 | Probe the sensor ground circuit with a unpowered test lamp connected to B+ at the harness connector. Does the test lamp illuminate? | -- | ||||||||
Is the Hz reading within the specified range? | 57-63 Hz | |||||||||
8 |
Did you perform a repair? | -- | ||||||||
9 |
Did you perform a repair? | -- | ||||||||
10 | Check the optical/fuel temperature 5 volt reference circuit for a faulty connection at the PCM and replace the terminal if necessary. Refer to Wiring Repairs in Wiring Systems. Did you perform a repair? | -- | ||||||||
Is the voltage within the specified range? | 4.8-5.2 V | |||||||||
12 | Is the voltage more than the specified value? | 5.2 V | ||||||||
13 | Repair the short to battery/ignition voltage on the CAM signal circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||||
14 |
Did you perform a repair? | -- | ||||||||
15 | Check for a proper connection at the PCM harness terminal and replace the terminal if necessary. Refer to Wiring Repairs in Wiring Systems. Did you perform a repair? | -- | ||||||||
With a DMM set to the mA scale, measure the current between the CAM signal circuit and the ground circuit at the optical/fuel temperature sensor electrical connector. Is the current less than the specified value? | 35mA | |||||||||
17 | Repair the short to reference voltage on the CAM signal circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||||
18 |
Did you perform a repair? | -- | ||||||||
19 |
Important: The new injection pump must be timed. Refer to Fuel Injection Pump Timing Adjustment . Replace the injection pump. Refer to Fuel Injection Pump Replacement . Is the action complete? | -- | -- | |||||||
|
Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the action complete? | -- | -- | ||||||||
21 |
Does the scan tool indicate the diagnostic Passed? | -- | ||||||||
22 | Does the scan tool display any additional undiagnosed DTCs? | -- | Go to the applicable DTC table | System OK |
