Circuit Description
The optical sensor provides a high resolution signal to the 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 three consecutive trips without a fault condition. |
| • | A History DTC will clear after forty consecutive engine warm up cycles, if this or any other emmision related diagnosic does not report any failures. |
| • | Use of a scan tool will clear the DTC codes. |
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. It is also possible that a P0251, P0370 and P1216 will 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 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 P0251 is also stored, the snap shot mode on the scan tool should be used in order to properly identify a malfunction. DTCs 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.
-
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 5 volts. A normal high res signal circuit will have 3-5 mA. Any reading over 50 mA indicates a short to 5 volts.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 |
Important: Before clearing any DTCs, use the scan tool Capture Info to save the Freeze Frame and Failure records for reference. The control module's data is deleted once the Clear Info function is used. Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||
Is the voltage at specified value? | 4.8-5.2 V | |||
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 (±100 Hz) with the Hertz reading on the DMM at the designated RPM? | -- | |||
6 |
Was the Optical sensor 5 volt reference circuit open or shorted to ground? | -- | ||
7 |
Did you perform a repair? | -- | ||
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. Did the terminal require replacement? | -- | ||
Is the voltage within the specified value? | 4.8-5.2 V | |||
10 | Is the voltage greater than the specified value? | 4.8-5.2 V | ||
11 | Repair the short to battery/ignition voltage on the high resolution signal circuit. Is the action complete? | -- | -- | |
12 |
Was a repair made? | -- | ||
With a J 39200 DMM set to the mA scale, measure the current between the High Res signal circuit and the ground circuit at the Optical/Fuel temperature sensor electrical connector. Is the current less than the specified value? | 50 mA | |||
14 | Repair the short to reference voltage on the high resolution signal circuit. Is the action complete? | -- | -- | |
15 |
Did you perform a repair? | -- | ||
16 |
Did you perform a repair? | -- | ||
17 | Replace the injection pump. Refer to Fuel Injection Pump Replacement Important: The new injection pump must be timed. Refer to Fuel Injection Pump Timing Adjustment . 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 |
