Seeing a check engine light can be stressful, especially when your car starts running rough or stalling at stoplights. When an OBD-II scanner pulls the meaning of code P1374, it usually points to a problem with the crankshaft position sensor or the ignition control module. Understanding this code matters because ignoring it can lead to sudden engine failure while driving, leaving you stranded on the side of the road.

What exactly does code P1374 mean?

Code P1374 is a manufacturer-specific OBD-II trouble code. You will see it most often on General Motors vehicles like Chevrolet, Buick, Pontiac, and GMC. The powertrain control module (PCM) sets this code when it detects an abnormal voltage or frequency in the 4X reference circuit. The PCM relies on the crankshaft position sensor to know exactly when to fire the spark plugs. If the signal is too high, too low, or completely missing, the engine computer cannot time the ignition correctly.

When will you notice this problem?

You typically encounter this issue when the vehicle is already showing signs of drivability problems. If you notice your dashboard warning light turns on along with a rough idle or hesitation during acceleration, you should scan the vehicle immediately. Other common symptoms include the engine stalling when coming to a stop, a severe lack of power, or a complete failure to start. Drivers use this code definition to understand why their ignition system is acting up and to decide if the car is safe to drive to a repair shop.

What causes the P1374 code to trigger?

Several electrical or mechanical issues can trigger this fault. Mechanics often find that frayed wiring or a failing sensor are the main culprits behind this electrical fault. The wiring harness running to the crankshaft position sensor is exposed to high heat and engine vibration, which can cause the insulation to crack over time. A faulty ignition control module is another frequent cause, especially on older GM 3.8L engines. Sometimes, the reluctor wheel on the crankshaft itself might have damaged teeth, preventing the sensor from reading the rotation accurately.

How do you figure out which part is broken?

Diagnosing this issue requires a methodical approach. Following a step-by-step troubleshooting process helps isolate whether the sensor or the module needs replacing. Start by visually inspecting the wiring harness and connectors near the crankshaft sensor. Look for corrosion, melted plastic, or exposed wires. Next, use a digital multimeter to check the resistance of the crankshaft position sensor and compare your readings to the manufacturer specifications. You can also use an oscilloscope to view the actual waveform of the 4X reference signal while the engine is cranking. When printing out your live data stream or freeze frame data to review later, choosing a highly legible typeface like Arial makes reading the voltage drops much easier.

Common mistakes people make when fixing this code

The biggest mistake DIY mechanics make is throwing parts at the problem. Replacing the crankshaft position sensor without testing the wiring harness first can cost you time and money, especially if the real issue is a broken wire hidden inside the loom. Another mistake is clearing the code with a scanner and assuming the problem is fixed. The code will almost always return if the underlying electrical fault is still present. Finally, using cheap aftermarket sensors instead of OEM parts often leads to repeated failures because the cheap sensors cannot handle the high-frequency signals the PCM requires.

Next steps to get your car running right

If your scanner shows the meaning of code P1374, take action before the engine completely stops running. Follow this practical checklist to get the vehicle fixed:

  • Scan the vehicle and record any additional codes, as codes related to the camshaft position sensor might point to a shared wiring issue.
  • Inspect the wiring harness leading to the crankshaft position sensor for physical damage, chafing, or oil contamination.
  • Test the sensor resistance with a multimeter to verify if it falls outside the factory specifications.
  • Check the ignition control module connections for corrosion and ensure the module is properly grounded to the engine block.
  • Replace the faulty component with a high-quality OEM part and clear the codes to verify the repair.