Circuit Description
The optical sensor provides a high resolution signal to the powertrain control module (PCM) by counting the pulses on the sensor disk which is located in the injection pump. The high resolution is one of the most important inputs by the PCM for the fuel control and the timing. This test monitors the number of high resolution pulses which have been missed (not detected). This test is based on a comparison between the number of pulses that were detected since the last pump cam pulse and the number of the pulses that should have occurred.
Conditions for Running the DTC
The engine is operating.
Conditions for Setting the DTC
A number of high resolution pulses missing (internal to the PCM) per every eight cam reference pulse.
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL) on the first drive trip 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 get below 1/8 of a tank while performing hard acceleration or turning maneuvers. Its also possible that a DTC P0251, P0370 and P1216 will set if vehicle has run out of fuel. Customer driving habits should be checked to determine if vehicle has been performing in these manners. If it has been determine that the vehicle has been performing in these conditions, bleed fuel system of all air and test drive vehicle.
When the PCM is in backup fuel, fast idle and poor performance problems will exist. If DTC P0251 is also stored, the snap shot mode on the scan tool should be used to in order to properly identify a malfunction. DTC P0335, P1216, and P1217 may set along with this DTC.
The least likely cause of failure is the PCM.
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
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This step will determine if the 5 volt reference is present.
-
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 and Failure Records can help create an active fault.
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This step determines if a High Res signal is being sent to the PCM. Refer to the RPM vs Hertz table to compare the Hertz readings at different RPMs. Using Freeze Frame and Failure Records will help identify the RPM the problem occurs.
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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..
-
This step determines if the signal circuit is shorted to 5V. A normal high res signal circuit will have 3-5mA. Any reading over 25mA indicates a short to 5V.
Step | Action | Value(s) | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
1 |
Important: Before clearing any DTCs, use the scan tool Capture Info function to save the Freeze Frame and the Failure records for reference. The control module's data is deleted once the Clear Info function is used. Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||||||||
Is the voltage at the specified value? | 4.8-5.2V | |||||||||
Is the test lamp ON? | -- | |||||||||
Does the scan tool display the term Last Test Failed? | -- | 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. Referring to the Engine Speed Versus Hertz (Hz) table, does the Hertz reading in the table correspond (plus or minus 100 Hz) with the Hertz reading on the DMM at the designated RPM? | -- | |||||||||
6 |
Did you perform a repair? | -- | ||||||||
7 |
Did you perform a repair? | -- | ||||||||
8 | Check the optical sensor 5 volt reference circuit for a poor connection at the PCM and replace the terminal if necessary. Refer to Wiring Repairs . Did you perform a repair? | -- | ||||||||
Is the voltage within the specified value? | 4.8-5.2V | |||||||||
10 | Is the voltage greater than the specified value? | 4.8-5.2V | ||||||||
11 | Repair the short to battery/ignition voltage on the high resolution signal circuit. Refer to Wiring Repairs . Is the action complete? | -- | -- | |||||||
12 |
Did you perform a repair? | -- | ||||||||
With a DMM J 39200 set to the mA scale, measure the current between the high resolution signal circuit and the ground circuit at the optical/fuel temperature sensor electrical connector. Is the current less than the specified value? | 25mA | |||||||||
14 | Repair the short to reference voltage on the high resolution signal circuit. Refer to Wiring Repairs . Is the action complete? | -- | -- | |||||||
15 |
Did you perform a repair? | -- | ||||||||
16 |
Did you perform a repair? | -- | ||||||||
17 |
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? | -- | -- | |||||||
18 |
Important: The new PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming . Replace the PCM. Is the action complete? | -- | -- | |||||||
19 |
Does the scan tool indicate the diagnostic Passed? | -- | ||||||||
20 | Does the scan tool display any additional undiagnosed DTCs? | -- | Go to the applicable DTC Table | System OK |
