Circuit Description
The optical sensor provides a high resolution signal to the powertrain control module (PCM) by counting pulses on the sensor disk located in the injection pump. This test monitors the number of high resolution pulses which have been missed. The test is based on a comparison between the number of pulses that were detected since the last pump cam pulse and the number of pulses that should have occurred. There are approximately 64 high resolution pulses for every cam pulse.
Conditions for Running the DTC
The engine is running.
Conditions for Setting the DTC
A number of high resolution pulses are missing (internal to PCM 64-to-1 ratio) per every 8 cam reference pulses.
Action Taken When the DTC Sets
| • | 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. |
Conditions for Clearing the MIL/DTC
| • | 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. |
Diagnostic Aids
Intermittent DTCs P0251, P0370 and P1216 may be caused by air entering the fuel system when fuel levels get below 1/8 of a tank while performing hard acceleration or turning maneuvers. However, a DTC P0251, P0370 and P1216 may set if the vehicle has run out of fuel. Customer driving habits should be checked 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 PCM is in backup fuel, fast idle and poor performance problems will exist. If DTC P0251 is also stored, the Snapshot mode on the scan tool should be used to properly identify the fault. DTCs P0335, P1216, and P1217 may set along with this DTC.
The least likely cause of failure is the PCM.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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This step will determine if the 5-volt reference is present.
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This step checks the ground circuit.
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This step determines if the problem is currently active by the scan tool displaying Last Test Failed. Do not proceed any further with this table if the scan tool does not display the term Last Test Failed. Duplicating the conditions in Freeze Frame/Failure Records can help create an active fault.
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This step determines if a High Resolution signal is being sent to the PCM. Refer to the RPM vs Hertz table to compare the Hertz readings at different RPMs. Using the Freeze Frame/Failure Records will help identify the problem.
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The PCM supplies 5 volts on the signal circuit. This step determines if that voltage is present, not present, or too much voltage is present.
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This step determines if the signal circuit is shorted to 5 volts. A normal high resolution signal circuit will have 3-5 mA. Any reading over 50 mA indicates a short to 5 volts.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |
Does the voltage measure within the specified range? | 4.8-5.2 V | Go to Step 3 | Go to Step 6 | |
Does the test lamp illuminate? | -- | Go to Step 4 | Go to Step 7 | |
Does the scan tool display Last Test Failed? | -- | Go to Step 5 | Go to Diagnostic Aids | |
Important: The scan tool must display Last Test Failed (under DTC, Specific). This ensures the fault is active while performing this test. Does the Hertz reading in Engine Speed Versus Hertz (Hz) correspond (±100 Hz) with the Hertz reading on the DMM at the given RPM? | -- | Go to Step 16 | Go to Step 9 | |
6 |
Did you find and correct the condition? | -- | Go to Step 19 | Go to Step 8 |
7 |
Did you find and correct the condition? | -- | Go to Step 19 | Go to Step 18 |
8 | Check the optical sensor 5-volt reference circuit for a proper connection at the PCM and replace the terminal if necessary. Refer to Wiring Repairs and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 19 | Go to Step 18 |
Does the voltage measure within the specified range? | 4.8-5.2 V | Go to Step 13 | Go to Step 10 | |
10 | Does the voltage measure more than the specified value? | 5.2 V | Go to Step 11 | Go to Step 12 |
11 | Repair the short to battery or ignition voltage on the high resolution signal circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 17 | -- |
12 |
Did you find and correct the condition? | -- | Go to Step 19 | Go to Step 16 |
Measure the current between the high resolution signal circuit and the low reference circuit at the optical/fuel temperature sensor electrical connector with a DMM set to the mA scale. Does the current measure less than the specified value? | 25 mA | Go to Step 15 | Go to Step 14 | |
14 | Repair the short to 5-volt reference voltage on the high resolution signal circuit. Did you complete the repair? | -- | Go to Step 19 | -- |
15 |
Did you find and correct the condition? | -- | Go to Step 19 | Go to Step 17 |
16 |
Did you find and correct the condition? | -- | Go to Step 19 | Go to Step 18 |
17 |
Important: The new injection pump must be timed. Refer to Fuel Injection Pump Timing Adjustment . Replace the fuel injection pump. Refer to Fuel Injection Pump Replacement . Did you compete the replacement? | -- | Go to Step 19 | -- |
18 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 19 | -- |
19 |
Does the DTC run and pass? | -- | Go to Step 20 | Go to Step 2 |
20 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |
