Code P1374 2003 Chevy Monte Carlo SS 3.8 liter engine No Spark

Hi Jaxer, My name is Bruce XXXXXX. My car was bucking and jerking at idle and a little black smoke was coming out the tailpipe. Now it has no spark and won’t start. Trouble code P/1374 was set. Crankshaft sensor 3x reference circuit.
I took an ac voltage measurement of the 3x crank sensor while cranking. I took the measurement at the ignition module where the sensor harness comes from the sensor to the module.
A light blue wire with a white stripe. It measured 1.7 to 2.8 ac volts. while cranking.
I measured the 18x signal wire, a yellow wire at the ignition module while cranking it shot right up to 3.5 ac volts with no minimum voltage. I used a digital multimeter. Wouldn’t the 18x wire reduce the voltage reading as it passes the open gaps on the reluctor wheel? Is my snap on multimeter too slow to read the change? Do I need a lab scope?
Can you check my voltage readings against a good service manual?
The ignition module has battery voltage reading on the pink wire and good ground.
The crank sensor has 10 volts while cranking and a good ground just like the manual said. 3 months ago i had an intermittent no start, cranked over fine. Engine would lope at idle, stall and upon restart it would idle and run fine.
If my signal wire voltages check out What’s an easy way to check an ignition module. Thanks a lot. Bruce XXXXXX

I have another question i saw online that if you turn the crankshaft by hand and measure the dc voltage on the 18x and 3x signal wires at the ignition module it should read o volts off and 5 to 6 volts on. what do you think of this test? bruce XXXXXX

My Thoughts

Sounds like you may have more than one thing going on here. After an initial read and thinking of all the common part failures for these. I think the no spark is ignition module replacement needed and the early on stalling were indication of this part failing. I noticed the p1374 code is different for the 3.4L and the 3.8L engine. So I added the Code P1374 info for the 3.8L Specific engine below. Easiest way to test an ignition module is to replace it. And with Free Returns options out there… Just sayin’. I did not find any information on testing the module in the manual.

The 3X reference signal is produced by the ignition control module (ICM). If the PCM detects an incorrect number of pulses on the 3X reference circuit, the DTC P1374 sets. So what I get from this would be the module is not doing its job and sets the code. Without the 3x reference(ICM) the PCM can not do its job(start the dang engine). You are getting readings on the wiring, so the wiring is most likely fine.

If it was mine, I would order a new module and try it to save time. I looked up the ignition module and found this one that comes with coils for about the some money. You figure the coils are probably just as old as the Ignition Module.

New Ignition Control Module

Code P1374 3.8L Specific

DTC P1374

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 18X pulses by 3 when the engine is running and CKP sync pulses are also being received. The powertrain control module (PCM) uses the 3X reference signal to calculate engine RPM and crankshaft position at engine speeds above 1,200 RPM. The PCM also uses the pulses on this circuit to initiate injector pulses. And the PCM constantly monitors the number of pulses on the 3X reference circuit and compares the number of 3X reference pulses to the number of 18X reference pulses and CAM signal pulses being received. The PCM will use the 18X reference signal circuit for fuel and ignition control. The engine will continue to start and run using the 18X reference and camshaft position PCM input signals only. If the PCM detects an incorrect number of pulses on the 3X reference circuit, DTC P1374 sets. Conditions for Running the DTC

The engine is running for more than 3 seconds. Conditions for Setting the DTC

• The ratio of 18X reference pulses to CAM signal pulses received by the PCM equals 36:1.
• The ratio of 18X reference pulses to 3X reference pulses received by the PCM does not equal 6:1.
• The above conditions are present for up to 30 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 System Check – Engine Controls

Description

The Diagnostic System Check is an organized approach to identifying a condition created by an electronic engine control system malfunction. The Diagnostic System Check must be the starting point for any driveability concern. The Diagnostic System Check directs the service technician to the next logical step in diagnosing the concern. Understanding the table and using the table correctly reduces diagnostic time and prevents the replacement of good parts.Test Description

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

2: Lack of communication may be due to a partial malfunction of the class 2 serial data circuit or due to a total malfunction of the class 2 serial data circuit. The specified procedure determines the particular condition.

5: This step stores the powertrain control module (PCM) diagnostic trouble code (DTC) information into the scan tools memory. Review the captured information at the end of the diagnostic procedure in order to catch the next DTC in the event there are multiple DTCs stored. It is beneficial to review the Freeze Frame/Failure Records data. Use this information in order to determine how frequently and how recently the DTC set. This information and other operating conditions when the DTC set may help diagnose an intermittent condition. Capturing the stored information preserves data that the PCM loses when the following occurs:

• When you are instructed to clear DTCs.
• The PCM connectors are disconnected.
• The PCM is replaced during a diagnostic procedure.

6: The presence of DTCs which begin with —U— indicate some other module is not communicating. The specified procedure will compile all the available information before tests are performed.

8: If there are other modules with DTCs set, refer to the DTC list. The DTC list directs you to the appropriate diagnostic procedure.

• Component level DTCs—Sensors, solenoids, relays etc. Multiple DTCs within this category should be diagnosed in numerical order starting with the lowest numbered DTC, unless otherwise directed.
• System level DTCs—Misfire, fuel trim, catalyst etc.

10: This step is for areas that have an Inspection/Maintenance or emission testing program. The testing facility found one or more I/M system statuses not set.