Refer to
Ignition System, Knock Sensor
.
Circuit Description
A 3X reference signal is produced by the ignition control (IC) module. The IC module calculates the 3X reference signal by dividing the crankshaft position (CKP) sensor 7X pulses by 2 when the engine is running and the CKP synchronizing pulses are being received. The powertrain control module (PCM) uses the 3X reference signal to calculate the engine RPM and the CKP at engine speeds above 1,600 RPM. The PCM also uses these pulses to initiate injector pulses. The PCM compares the 3X reference pulses to the 24X CKP pulses and the camshaft position (CMP) pulses. The PCM will use the 24X CKP reference circuit for fuel and ignition control. The engine will continue to start and run using only the 24X CKP and CMP sensor signals. If the PCM detects an incorrect number of pulses on the low resolution engine speed signal circuit, DTC P1374 sets.
Conditions for Running the DTC
The engine is running (24X reference pulses are being received).
Conditions for Setting the DTC
| • | The ratio of 24X reference pulses to CAM signal pulses received by the PCM equals 48:1. |
| • | The ratio of 24X reference pulses to 3X reference pulses received by the PCM does not equal 8:1. |
| • | Above conditions for 30 seconds. |
Action Taken When the DTC Sets
| • | The PCM will illuminate the MIL during the second consecutive trip in which the DTC test has run and failed. |
| • | The PCM will use the 18X reference signal circuit for fuel and ignition control. |
| • | If equipped with traction control, the PCM will command the EBTCM via serial data (CKT 800) to turn OFF traction control, and the EBTCM will illuminate the TRACTION OFF lamp. |
| • | The PCM will store conditions which were present when the DTC set as Freeze Frame and Fail Records data. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn the MIL OFF during the third consecutive trip in which the diagnostic has been run and passed. |
| • | The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction. |
| • | The DTC can be cleared by using the scan tool Clear Info function or by disconnecting the PCM battery feed. |
Diagnostic Aids
An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation. Check for:
| • | Poor connection. Inspect the PCM harness and connectors for improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection,. |
| • | Damaged harness. Inspect the wiring harness for damage. If the harness appears to be OK, disconnect the PCM, turn the ignition ON and observe a J 39200 connected to the 3X reference circuit at the PCM harness connector while moving connectors and wiring harnesses related to the ICM. A change in voltage will indicate the location of the fault. |
Reviewing the Fail Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Was the Powertrain On-Board Diagnostic System Check performed? | -- | ||
2 | Attempt to start the engine. Does the engine start and continue to run? | -- | ||
3 |
Does the scan tool indicate DTC P1374 failed this ign? | -- | Refer to Diagnostic Aids | |
4 |
Does the injector test light blink? | -- | ||
5 |
Was a problem found? | -- | ||
6 |
Did terminal need to be replaced? | -- | ||
7 | Check for the following conditions:
Was a problem found? | -- | ||
8 |
Did any terminals need to be replaced? | -- | ||
9 | Replace the Ignition Control Module (ICM). Refer to Ignition Control Module Replacement . Is action complete? | -- | -- | |
Replace the PCM. Important: Replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming . Is action complete? | -- | -- | ||
11 |
Does scan tool indicate DTC P1374 failed? | -- | System OK |
