DTC P1374 Crankshaft Position (CKP) High to Low Resolution Frequency Correlation. Buick GL7 (Export) 2000

For 1990-2009 cars

### Circuit Description

The 3X reference signal is produced by the ignition control module (ICM). The ICM 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 of more than 1600±150 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. 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 control and ignition control. The engine will continue to start and run using only the 24X CKP and CMP sensor signals.

### Conditions for Running the DTC

The engine is running and 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 and Failure Records data.

### Conditions for Clearing the MIL/DTC

• | The PCM will turn OFF the MIL 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.

### Diagnostic Aids

Inspect or test for the following conditions:

• | DTC P1374 can be caused by secondary components leaking high voltage into the ICM. Inspect for the following conditions:

- | An incorrect harness routing near secondary ignition components

- | An ignition coil arcing to the wiring harness or the ICM. Check the ignition coils for cracks, carbon tracking, or other signs of damage.

- | Any secondary ignition wires arcing to the wiring harness

• | A poor connection. Inspect the PCM harness and the connectors for the following conditions. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems:

- | Backed-out terminals

- | Improper mating

- | Broken locks

- | Improperly formed or damaged terminals

- | Poor terminal-to-wire connection

• | A 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 digital multimeter (DMM) connected to the 3X reference circuit at the PCM harness connector while moving the connectors and the wiring harnesses related to the ICM. A change in the voltage indicates the location of the fault. Refer to Wiring Repairs in Wiring Systems .

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

1. | After the MAP sensor freezes, DTC P0121 Throttle Position (TP) Sensor Performance may set due to the incorrect MAP value, and the engine may be difficult to start.

2. | After a long crank 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.

Reviewing the Failure 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

The number below refers to the step number on the diagnostic table

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

#### DTC P1374 - 3X Reference Circuit

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 the scan tool Failure Records data.
2. Operate the vehicle within the Failure Records conditions as noted.
3. Monitor the 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. Turn ON the ignition switch.
2. Connect a test lamp to B+.
3. Repeatedly touch the test lamp to the 3X reference high circuit at the ICM harness connector while observing the 3x reference scan tool display.

Is RPM indicated by the 3x reference parameter?

--

Go to Step 8

Go to Step 5

5

1. Turn OFF the ignition switch.
2. Disconnect the PCM.
3. Turn ON the ignition switch.

Test for the following conditions:

• | An open in the 3X reference high circuit

• | A short to ground in the 3X reference high circuit

• | A short to voltage in the 3X reference high circuit

4. If a problem is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a problem found?

--

Go to Step 11

Go to Step 6

6

1. Test the 3X reference circuits for a poor terminal connection at the PCM.
2. If a problem is found, replace the faulty terminal. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Was a problem found?

--

Go to Step 11

Go to Step 7

7

1. Test for the following conditions:

• | An incorrect harness routing near any secondary ignition components

• | An ignition coil arcing to the wiring harness or to the ICM. Inspect the ignition coils for cracks, carbon tracking, or other signs of damage.

• | Any secondary ignition wires arcing to the wiring harness

2. If a problem is found, repair as necessary.

Was a problem found?

--

Go to Step 11

Go to Step 10

8

1. Test for faulty terminal connections at the ICM.
2. If a problem is found, replace the faulty terminals as necessary. Refer to Push to Seat Connectors in Wiring Systems.

Was a problem found?

--

Go to Step 11

Go to Step 9

9 | Replace the ignition control module. Is the action complete? | -- | Go to Step 11 | --
10 | Important: : The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the action complete? | -- | Go to Step 11 | --

11

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

Does the scan tool indicate DTC P1374 failed?

--

Go to Step 2

System OK