For 1990-2009 cars

Refer to

#### Ignition System, Knock Sensor

Engine Controls Components
Powertrain Control Module Description
Fuel Control
Power, Ground, MIL, DLC
OBD II Symbol Description Notice
Engine Controls Connector End Views
Cell 10: Underhood Accessory Wiring Junction Block
ESD Notice
.

### Circuit Description

The 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 PCM uses the 3X reference signal to calculate the engine RPM and the crankshaft position at engine speeds above 1600 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 CMP pulses. If the PCM receives an incorrect number of pulses on the 3X circuit a DTC P1374 will set and 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 camshaft position (CMP) sensor signals.

### 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 3X reference pulses received by the PCM does not equal 8.

• | The ratio of 24X reference pulses to camshaft position 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 PCM will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed.

• | The PCM will store conditions which were present when the DTC set as Freeze Frame/Failure Records data.

### Conditions for Clearing the MIL/DTC

• | The PCM will turn OFF the malfunction indicator lamp (MIL) during the third consecutive trip in which the diagnostic has 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 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

- | Any other signs of damage

• | Secondary ignition wires arcing to wiring harness

• | The MAP sensor reading will freeze when the 3X signal is lost.

| After the MAP sensor freezes, DTC P0101 Mass Air Flow (MAF) Sensor Performance may set due to the incorrect MAP value and the engine may be hard to start (possible long crank).

| Eventually (after a long crank) a DTC P0108 Manifold Absolute Pressure (MAP) Sensor Circuit High Voltage may also set and replace the MAP sensor value with a default value and the engine will start and regain some performance.

Many situations may lead to an intermittent condition. Perform each inspection or test as directed.

Important: : Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.

• | Loose terminal connection

- | Use a corresponding mating terminal to test for proper tension. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair.

- | Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair.

• | Damaged harness--Inspect the wiring harness for damage. If the harness inspection does not reveal a problem, observe the display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the scan tool display may indicate the location of the fault. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair.

• | Inspect the powertrain control module (PCM) and the engine grounds for clean and secure connections. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair.

If the condition is determined to be intermittent, reviewing the Snapshot or Freeze Frame/Failure Records may be useful in determining when the DTC or condition was identified.

### Test Description

The numbers below refer to the step numbers on the diagnostic table:

1. This vehicle is equipped with a PCM which utilizes an electrically erasable programmable read only memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed.

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Powertrain On Board Diagnostic (OBD) System Check? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 | Attempt to start the engine. Does the engine start and continue to run? | -- | Go to Step 3 | Go to Engine Cranks but Does Not Run
3 |

1. Review and record scan tool Fail Records data.
2. Operate the vehicle within Fail Records conditions as noted.
3. Monitor Specific DTC info for DTC P1374 on the scan tool.

Does the scan tool indicate DTC P1374 failed this ignition?

--

Go to Step 4

Go to Diagnostic Aids

4 |

1. Install J 34730-380 Injector Harness Load Tester using J 34730-410 Load Tester Adaptor to the multi-way fuel injector harness connector.
2. Turn ON the ignition.
3. Connect a test lamp to ground.
4. Repeatedly touch the test lamp to the 3X reference high circuit at the ignition control (IC) module harness connector while observing the J 34730-380 Injector Harness Load Tester.

Does the J 34730-380 lights blink?

--

Go to Step 8

Go to Step 5

5 |

1. Turn the ignition OFF.
2. Disconnect the PCM.
3. Turn the ignition ON.
4. Test for the following conditions:

• | 3X reference high circuit open

• | 3X reference high circuit shorted to ground

• | 3X reference high circuit shorted to voltage--Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 11

Go to Step 6

6 | Test the 3X reference circuits for a poor terminal connection at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 7
7 | Test for the following conditions:

1. Incorrect harness routing near secondary ignition components
2. Ignition coil arcing to the wiring harness or to the ignition control (IC) module--Inspect the ignition coils for cracks, carbon tracking, or other signs of damage.
3. Secondary ignition wires arcing to the wiring harness

Did you find and correct the condition?

--

Go to Step 11

Go to Step 10

8 | Test for faulty terminal connections at the ignition control (IC) module. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 9
9 | Replace the ignition control (IC) module. Refer to Ignition Control Module Replacement . Did you complete the replacement? | -- | Go to Step 11 | --
10 | Important: : The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Did you complete the replacement? | -- | Go to Step 11 | --
11 |

1. Review and record scan tool Fail Records data.
2. Clear DTCs.
3. Operate the vehicle within Fail Records conditions as noted.
4. Using a scan tool, monitor Specific DTC info for DTC P1374.

Does the scan tool indicate DTC P1374 failed?

--

Go to Step 2

System OK