P0370

Diagnostic Chart:

Wiring Diagram:

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. This is a type A DTC.

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
Backup fuel.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The PCM will turn the Malfunction Indicator Lamp (MIL) off after three consecutive trips without a fault condition.
^ A History DTC will clear after forty consecutive warm-up cycles during which the diagnostic does not fail (the coolant temperature has risen 5°C (40°F) from the start up coolant temperature and the engine coolant temperature exceeds 71°C (160°F) during that same ignition cycle).
^ Use of a Scan Tool will clear the DTC codes.

DIAGNOSTIC AIDS
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 to in order to properly identify a malfunction. A P0370 may set if the vehicle runs out of fuel. DTCs P0335, P1216, and P1217 may set along with this DTC.
The least likely cause of failure is the PCM.

TEST DESCRIPTION
The number(s) below refer to the Step number(s) on the Diagnostic Table.
2. This Step will determine if there is a 5 volt reference.
3. This Step checks the ground circuit.
4. This Step will check to see if the sensor is sending a signal back to the PCM.

***This is TSB update 67-65-39, dated January 1997****

Subject:
Intermittent Malfunction Indicator Lamp (MIL) with DTCs P0251, P0370, P1216 and Stumble, Stall, Hard Start (Check Fuel Tank Level)

Condition
Some owners may experience an intermittent Malfunction indicator Lamp (MIL) associated with history DTC's P0251, P0370, P1216. Also, owners may experience a stumble, hard start or stall. It is possible that the technician may not be able to duplicate the driveability concern but will notice history DTCs on the Tech 2 scanner.

Cause
Air entering the fuel system when fuel levels get below 1/8 of a tank during hard acceleration or turning maneuvers.

Correction
Check fuel tank level, if necessary fill tank to at least 1/2 full and purge air from fuel system using procedure in Service Manual. Erase DTCs on Tech 2 scanner. Additionally, inform customer of conditions associated with low fuel levels indicated in the Diesel Supplement Owner's Manual.