Schematic Reference: Engine Controls Schematics
Circuit Description
The distributor ignition system supplies two timing inputs to the PCM, a high resolution signal (180 pulses per one crankshaft revolution) and a low resolution signal (4 pulses per one crankshaft revolution). The PCM can determine if one of the timing inputs is not being received by comparing the two inputs. If the PCM detects the high resolution timing pulse without detecting the low resolution timing pulse, DTC P1371 will set.
The high and low resolution circuits toggle between 0 and 5 volts as the camshaft turns. The following malfunctions to the low resolution circuit will cause a DTC P1371 to set:
| • | An open. |
| • | A short to voltage. |
| • | A short to ground. |
| • | A defective ignition module within the distributor. |
Conditions for Setting the DTC
| • | The PCM detects a predetermined amount of high resolution pulses before detecting any low resolution pulses. |
Action Taken When the DTC Sets
| • | The PCM will illuminate the Malfunction Indicator Lamp (MIL) when the diagnostic runs and fails. |
| • | The PCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and/or Failure Records. |
| • | The injector will be disabled for the entire ignition cycle. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn the MIL OFF after three consecutive drive trips that the diagnostic runs and does not fail. |
| • | A last test failed (Current DTC) will clear when the diagnostic runs and does not fail. |
| • | A History DTC will clear after forty consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | PCM battery voltage is interrupted. |
| • | Using a Scan tool. |
Diagnostic Aids
| • | For any test that requires probing the PCM or a component harness connector, must use the Connector Test Adapter Kit J 35616-A. Using this kit will prevent damage to the harness connector terminals. |
| • | DTC P1371 will set if the high and low resolution circuits are shorted together. Before replacing any components, inspect the low and high resolution circuits for being shorted. |
| • | When an intermittent DTC P1371 occurs, a misfire will be apparent. To locate an intermittent, use the scan tools snapshot feature. Try to duplicate the conditions under which the misfire is present. When reviewing captured data, watch for any abnormal high and low resolution timing pulses. |
| • | If DTC P1351 and/or DTC P1361 is also set with a DTC P1371, and no external fault can be found, replace the PCM. If only DTC P1371 is set and the distributor connections are OK, replace the distributor. |
| • | If distributor components must be replaced, check distributor vent system operation. Refer to Distributor Ignition System. |
| • | If a DTC P1371 is not present and a no start condition is present, Refer to Engine Cranks But Does Not Run . |
| • | For intermittents, refer to Symptoms . |
Test Description
Number(s) below refer to step numbers on the diagnostic table.
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This step verifies if the malfunction is active. If the engine starts, the malfunction is not present at this time.
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If the harness and connections check out OK, but the engine stalls after reaching higher operating temperatures, return to Step 2 and test the system while the fault is present.
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Normal voltage may vary slightly from the specified value. A value that is significantly higher or lower indicates a problem. This step isolates the circuit between the test connector and the PCM.
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Normal voltage may vary slightly from the specified value. A value that is significantly higher or lower indicates a problem. This step isolates the circuit between the test connector and the distributor.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||
Does the scan tool indicate RPM while cranking the engine? | -- | |||
Does the engine cut out or stall while moving the various components. | -- | Go to Diagnostic Aids | ||
Does the DVM indicate the voltage specified? | 5 V | |||
Does the DVM indicate voltage specified? | 5 V | |||
6 | Is voltage higher than the specified value? | 5 V | ||
7 | Repair the short to voltage on Low Resolution signal circuit from PCM to ignition system test connector. Is the action complete? | -- | -- | |
8 | Is the voltage higher than the specified value? | 5 V | ||
9 | Repair the open or grounded Low Resolution circuit from the ignition system test connector to the PCM. Was the condition found and repaired? | -- | ||
10 | Repair the short to voltage on Low resolution signal circuit from ignition system test connector to Distributor. Is the action complete? | -- | -- | |
11 | Repair the faulty Distributor connection or faulty Distributor. Is the action complete? | -- | -- | |
12 | Repair the open or grounded Low Resolution circuit from ignition system test connector to the Distributor. Was the condition found and repaired? | -- | ||
13 | Repair the harness/connections as necessary. Is the action complete? | -- | -- | |
14 |
Important:: Replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming . Replace the PCM. Is the action complete? | -- | -- | |
15 |
Does the scan tool indicate that this test ran and passed? | -- | ||
16 | Using the scan tool, select Capture Info, Review Info. Are any DTCs displayed that have not been diagnosed? | -- | Go to the applicable DTC table | System OK |
