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DTC P1374 Crankshaft Position (CKP) High to LowResolution Frequency Correlation

Refer to Ignition Controls.

Circuit Description

A 3X reference signal is produced by the ignition control (IC) module. The IC module calculates the 3X refereignal by dividing the crankshaft position (CKP) sensor 7X pulses by 2 when the engine is running and the CKynchronizing pulses are being received. The powertrain control module (PCM) uses the 3X reference signal t

calculate the engine RPM and the CKP at engine speeds above 1,600 RPM. The PCM also uses these pulses tonjector pulses. The PCM compares the 3X reference pulses to the 24X CKP pulses and the camshaft position

pulses. The PCM will use the 24X CKP reference circuit for fuel and ignition control. The engine will continuand run using only the 24X CKP and CMP sensor signals. If the PCM detects an incorrect number of pulses onesolution engine speed signal circuit, DTC P1374 sets.

Conditions for Setting the DTC

The engine is running (24X reference pulses are being received). 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

Action Taken When the DTC Sets

The PCM will illuminate the MIL during the second consecutive trip in which the diagnostic test has beeand failed.

The PCM will store conditions which were present when the DTC set as Freeze Frame and Fail Records The MAP Sensor reading will freeze when the 3X signal is lost. (Refer to Diagnostic Aids for further op

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 apassed.

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

DTC P1374 can be caused by secondary components leaking high voltage into the ignition module. Check for

following conditions:

Incorrect harness routing near secondary ignition components; Ignition coil arcing to wiring harness or Ignition Control Module (check ignition coils for cracks, carbon

tracking, or other signs of damage); Secondary ignition wire(s) arcing to wiring harness.

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside thnsulation. Check for:

Poor connection. Inspect the PCM harness and connectors for improper mating, broken locks, improperl

Document ID# 65016

1997 Pontiac Grand Am

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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 th

turn the ignition ON and observe a voltmeter connected to the 3X reference circuit at the PCM harness cwhile moving connectors and wiring harnesses related to the ICM. A change in voltage will indicate the of the fault.

The MAP Sensor reading will freeze when the 3X signal is lost.1. After the MAP sensor freezes, DTC P0101 will set due to the incorrect MAP Value and the engin

hard to start (possible long crank).2. Eventually (after a long crank) a DTC P0108 will also set and replace the MAP Sensor value with

value and the engine will start and regain some performance.

Reviewing the Fail Records vehicle mileage since the diagnostic test last failed may help determine how oftencondition 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.

10. This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only M(EEPROM). When the PCM is being replaced, the new PCM must be programmed.

DTC P1374 - 3X Reference Circuit

Step ActionValue

(s) Yes No

1Was the Powertrain On-Board Diagnostic (OBD) System Checkperformed?

--Go toStep 2

Go to PowOBD System

2Attempt to start the engine.

Does the engine start and continue to run?

-- Go toStep 3

Go to EnCranks bu

Not R

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 ign?

--

Go toStep 4

Refer to DiAid

4

1. Install J 34730-380 using J 34730-385 adaptor to the 10-way fuelinjector harness connector.

2. Turn on the ignition switch.3. Connect a test light to ground.4. Repeatedly touch the test light to the 3X reference high circuit at

the ignition control module harness connector while observing theinjector test light.

Does the injector test light blink?

--

Go toStep 8 Go to S

5

1. Turn off the ignition switch.2. Disconnect the PCM.3. Turn on the ignition switch.4. Check for the following conditions:

3X reference circuit open. 3X reference circuit shorted to ground. 3X reference circuit shorted to voltage.

5. If a problem is found, repair as necessary. Refer to Wiring Repair inElectrical Diagnosis.

--

Go to

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Was a problem found? Step 11 Go to S

6

Check the 3X reference circuit for a poor terminal connection at thePCM.

If a problem is found, replace faulty terminal. Refer to WiringRepair in Electrical Diagnosis.

Was a problem found?

--

Go toStep 11 Go to S

7

1. Check for the following conditions: Incorrect harness routing near secondary ignition

components. Ignition coil arcing to the wiring harness or to the ignition

control module (check the ignition coils for cracks, carbontracking, or other signs of damage).

Secondary ignition wire(s) arcing to the wiring harness.2. If a problem is found, repair as necessary.

Was a problem found?

--

Go toStep 11 Go to St

8

1. Check for faulty terminal connections at the Ignition ControlModule (ICM).

2. If a problem is found, replace faulty terminals as necessary. Referto Wiring Repair in Electrical Diagnosis.

Was a problem found?

--

Go toStep 11 Go to S

9Replace the ignition control module. Refer to Ignition Control Module.

Is action complete?

-- Go toStep 11 --

10

Replace the PCM.

Important:

The replacement PCM must be programmed. Refer to PCM

Replacement/Programming Replacement.

Is the action complete?

--

Go toStep 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 toStep 2 System

Document ID# 650161997 Pontiac Grand Am