I remember when the Quad 4 engine first came out and thinking what a pain in the ass diagnosing and repairing it would be. And as time went on, I found out just how right that first impression was.
Well, in this article I've made diagnosing the ignition control module (ICM) and the crankshaft position sensor (7X CKP) as easy and as pain free as possible. With this test, you'll be able to pinpoint the problem to the ignition control module (ICM) or the crankshaft position sensor (7X CKP Sensor).
Before starting the tests you must first check and verify that there's NO SPARK present at any of the coil towers causing the car NOT TO START. Why? Because this article only shows you how to test the ignition control module/CKP Sensor and not the ignition coils. If your car cranks and starts, but runs with a misfire and you need to test the ignition coils, the following tutorials will help:
For the ignition control module tests for the 2.2L GM engine, go here:
For more info on the basics of troubleshooting a no start condition, I recommend the following tutorial:
- How To Troubleshoot A No Start (GM 2.3L, 2.4L Quad 4) (at: troubleshootmyvehicle.com).
You can find this tutorial in Spanish here: Cómo Probar El Módulo de Encendido y Sensor del Cigüeñal (GM 2.4L) (at: autotecnico-online.com).
Basic Operating Theory
Here is a little background information to help you diagnose this no spark condition. In a nutshell, when the system is working properly, at crank-up and at all engine speeds, the ECM (Fuel Injection Computer) controls both ignition coils thru' the ignition control module (ICM). How?
- As the engine cranks and starts, the ignition control module (ICM) receives the Crankshaft Position (7X CKP) Sensor Signal.
- This Crank Sensor Signal is an AC voltage signal that the ignition module now transforms into a Digital Signal and sends it to the fuel injection computer.
- The fuel injection computer, upon receiving this modified Crank Sensor Signal (which GM calls the 7X REFERENCE Signal), creates two separate Ignition Coil Control Signals that it sends back to the ignition control module.
- These Ignition Coil Control Signals are the ones that the ignition module uses to start sparking the two ignition coils that are connected to it.
- One Ignition Control Signal is for the ignition coil that fires cylinders 1 and 4 and the other for the one that fires cylinders 2 and 3.
- Also, with this 7X REFERENCE Signal, the fuel injection computer knows when to start activating the fuel injectors.
OK, the only thing you have to remember from all of this is the difference between the 7X CKP Signal and the 7X REFERENCE Signal. There'll be a quiz at the end of the article.
Where Do We Start?
We'll first check for the basics like battery voltage and engine Ground to the ignition control module. Then we'll test the 7X crankshaft position sensor signals, the 7X REFERENCE Signal and the ignition coil control signals (from the ECM to the module) in action and from the results you get you'll be able to pinpoint the problem to the ignition control module or the crankshaft position sensor or completely eliminate these as the cause of the no start condition.
IMPORTANT- All of the tests are ON CAR TESTS, do not remove the coil/module assembly from the vehicle (all of the figures show the coil module assembly off of the car but this is just for illustration purposes only). And lastly, this Fast Test only tests for a no start condition.
What Tools Do I Need?
No expensive diagnostic equipment is needed. You don't even need a scan tool. In case you're one of the privileged few who owns an oscilloscope, I have included photos of what the waveforms should look like. Whether you use a multimeter or an oscilloscope, you'll be able to successfully diagnose this no-start condition! So, read on my friend.
- A digital multimeter that can read Hertz (Hz) Frequency.
- This multimeter, that can read Hertz Frequency, is a must have or you won't be able to accomplish some of these tests. (don't have a digital multimeter that can read Hertz frequency? Click here to see my recommendations: Buying A Digital Multimeter For Automotive Diagnostic Testing).
- A helper
- To help you crank the engine.
- A repair manual.
- For any info that's not covered in this article.
Test Info: The Circuit Descriptions
Here are brief descriptions of the circuits that we'll be testing. The ignitoin control module harness connector will have the same letters on it.
- A- WHITE wire. 1-4 Ignition Coil Control Signal (comes from the ECM).
- B- ORANGE wire. 2-3 Ignition Coil Control Signal (comes from the ECM).
- C- Empty. No circuit exists.
- D- Empty. No circuit exists.
- E- Empty. No circuit exists.
- F- YELLOW wire. crankshaft position sensor circuit.
- G- PURPLE with WHITE stripe wire. 7X Reference Signal (goes to the ECM).
- H- RED with BLACK stripe wire. ground circuit for ECM.
- J- PURPLE wire. crankshaft position sensor circuit.
- K- BLACK wire. engine ground (for the module).
- L- PINK wire. 12 Volts with ignition ON.
Now, don't worry, it's lots of wires but you'll see just how easy it is to test this module. All right, lets get started!