For 1990-2009 cars

### 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 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, and the 24X reference pulses are being received.

### Conditions for Setting the DTC

• | The ratio of 24X reference pulses to 3X reference pulses received by the PCM does not equal 8.

• | The ratio of 24X reference pulses to CMP PCM input pulses received by the PCM equals 48.

• | The conditions are present for more than 10 seconds.

### Action Taken When the DTC Sets

• | The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.

• | The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

### Conditions for Clearing the MIL/DTC

• | The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.

• | A current DTC, Last Test Failed, clears when the diagnostic runs and passes.

• | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.

• | Clear the MIL and the DTC with a scan tool.

### Diagnostic Aids

DTC P1374 can be caused by secondary components leaking high voltage into the IC module.

Inspect for the following conditions:

• | Incorrect harness routing near secondary ignition components

• | Ignition coil arcing to wiring harness or IC module--Inspect the ignition coils for the following conditions:

- | Cracks

- | Carbon tracking

- | Other signs of damage

• | Secondary ignition wires arcing to the wiring harness

• | If the DTC is determined to be intermittent, refer to Intermittent Conditions .

Step | Action | Yes | No
--- | --- | --- | ---
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Controls Connector End Views or Powertrain Control Module Connector End Views
1 | Did you perform the Diagnostic System Check-Engine Controls? | Go to Step 2 | Go to Diagnostic System Check - Engine Controls
2 | Attempt to start the engine. Does the engine start and run? | Go to Step 4 | Go to Step 3
3 |

1. Observe the Freeze Frame/Failure Records for this DTC.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine.
4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Does the DTC fail this ignition?

Go to Step 4

Go to Diagnostic Aids

4 |

1. Turn OFF the ignition.
2. Disconnect the 6-way ignition control module connector.
3. Remove the injector fuse.
4. Turn ON the ignition, with the engine OFF.
5. Momentarily probe the low resolution engine speed signal circuit at the ignition module harness connector with a test lamp connected to B+.
6. Observe the Engine Speed parameter with a scan tool.

Is an Engine Speed displayed?

Go to Step 8

Go to Step 5

5 | Did the test lamp illuminate? | Go to Step 7 | Go to Step 6
6 |

1. Turn OFF the ignition.
2. Disconnect the PCM.
3. Turn ON the ignition, with the engine OFF.
4. Test the low resolution engine speed signal circuit of the ignition control module for the following conditions:

• | An open

• | A short to voltage

• | High resistance

Refer to Wiring Repairs and Circuit Testing in Wiring Systems.

Did you find and correct the condition?

Go to Step 12

Go to Step 9

7 |

1. Turn OFF the ignition.
2. Disconnect the PCM.
3. Test the low resolution engine speed signal circuit of the ignition control module for a short to ground or high resistance. Refer to Wiring Repairs and Circuit Testing in Wiring Systems.

Did you find and correct the condition?

Go to Step 12

Go to Step 9

8 | Test for an intermittent and for a poor connection at the ignition control module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 12 | Go to Step 10
9 | Test for an intermittent and for a poor connection at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 12 | Go to Step 11
10 | Replace the ignition control module. Refer to Ignition Control Module Replacement . Did you complete the replacement? | Go to Step 12 | --
11 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | Go to Step 12 | --
12 |

1. Clear the DTCs with a scan tool.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine.
4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

Go to Step 2

Go to Step 13

13 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | Go to Diagnostic Trouble Code (DTC) List | System OK