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.
The engine is operating.
Eight consecutive cam pulses are missing.
or
An average of eight cam pulses are missing.
• | The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails. |
• | The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/Failure Records. |
• | The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
• | A current DTC, Last Test Failed, clears when the diagnostic runs and passes. |
• | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
• | Clear the MIL and the DTC with a scan tool. |
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 DTC 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 the following conditions:
• | Faulty connections |
• | Rubbed-through wire insulation |
• | Broken wire inside the insulation |
Review Freeze Frame/Failure Records. If code P0251 is set at 0 RPM, the code is false and should be ignored.
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.
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.
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.
Step | Action | Values | Yes | No | ||||||
---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||||||||
1 |
Important: Before clearing the DTCs, use the scan tool Capture Info to save the Freeze Frame/Failure Records for reference. The data in the control module is deleted once the Clear Info function is used. Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |||||||
2 | Is DTC P0370 set also? | -- | Go to DTC P0370 | Go to Step 3 | ||||||
Does scan tool display the specified value? | 8 | Go to Step 5 | Go to Step 4 | |||||||
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 Diagnostic Aids | |||||||
Does the voltage measure within the specified range? | 4.8-5.2 V | Go to Step 6 | Go to Step 8 | |||||||
6 | Probe the sensor ground circuit with an J 35616-200 Unpowered Test Light connected to B+ at the harness connector. Does the test lamp illuminate? | -- | Go to Step 7 | Go to Step 9 | ||||||
Is the Hz reading within the specified range? | 57-63 Hz | Go to Step 15 | Go to Step 11 | |||||||
8 |
Did you perform a repair? | -- | Go to Step 21 | Go to Step 10 | ||||||
9 |
Did you perform a repair? | -- | Go to Step 21 | Go to Step 15 | ||||||
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? | -- | Go to Step 21 | Go to Step 20 | ||||||
Does the voltage measure within the specified range? | 4.8-5.2 V | Go to Step 16 | Go to Step 12 | |||||||
12 | Does the voltage measure more than the specified value? | 5.2 V | Go to Step 13 | Go to Step 14 | ||||||
13 | Repair the short to battery/ignition voltage on the CAM signal circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 21 | -- | ||||||
14 |
Did you perform a repair? | -- | Go to Step 21 | Go to Step 15 | ||||||
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? | -- | Go to Step 21 | Go to Step 20 | ||||||
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. Does the current measure less than the specified value? | 35 mA | Go to Step 18 | Go to Step 17 | |||||||
17 | Repair the short to reference voltage on the CAM signal circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 21 | -- | ||||||
18 |
Did you perform a repair? | -- | Go to Step 21 | Go to Step 19 | ||||||
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 . Did you complete the replacement? | -- | Go to Step 21 | -- | ||||||
20 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 21 | -- | ||||||
21 |
Does the scan tool indicate the diagnostic passed? | -- | Go to Step 22 | Go to Step 2 | ||||||
22 | Does the scan tool display any additional undiagnosed DTCs? | -- | System OK |