I think you'll be quite impressed with how easy it is to test both the ignition control module (ICM) and the distributor pickup coil to see if either of them have failed.
In this tutorial, you'll find the test steps explained step by step. Based on your test results, you can quickly determine if the ICM or distributor pickup coil is defective and causing the engine not to start.
Contents of this tutorial:
- Symptoms Of A Bad Ignition Control Module Or Pickup Coil.
- Ignition Control Module Circuit Descriptions.
- Where To Buy The Ignition Control Module And Save.
- What Tools Do I Need To Test The ICM And Distributor Pickup Coil?
- TEST 1: Making Sure The ICM Is Getting 12 Volts.
- TEST 2: Testing The Ignition Coil Control Signal.
- TEST 3: Testing The Pickup Coil Signal.
- Distributor Pickup Coil Waveform.
- More 2.5L Chevy S10 Pickup, GMC S15 Pickup, And GMC Sonoma Tutorials.
You can find this tutorial in Spanish here: Cómo Probar El Módulo De Encendido (1989-1993 2.5L Chevrolet S10 Pickup, GMC S15 Pickup, GMC Sonoma) (at: autotecnico-online.com).
APPLIES TO: This tutorial applies to the following vehicles:
- 2.5L Chevrolet S10 Pickup: 1989, 1990, 1991, 1992, 1993.
- 2.5L GMC S15 Pickup: 1989, 1990.
- 2.5L GMC Sonoma: 1991, 1992, 1993.
Symptoms Of A Bad Ignition Control Module Or Pickup Coil
If the ignition control module or distributor pickup coil fails, the engine will generally not start because of a lack of spark.
To be more specific, the engine will not start because all four spark plugs do not spark to ignite the air/fuel mixture in their cylinders.
In some cases, the ICM or distributor pickup coil will fail intermittently. In other words, they'll work fine most of the time, but not every now and then.
Ignition Control Module Circuit Descriptions
The ignition control module has three connectors. Here's a brief description of the circuits (wires) of all three connectors:
| CONNECTOR 1 | ||
|---|---|---|
| Terminal | Wire | Description |
| + | Pink (PNK) or pink with black stripe (PNK/BLK) | 12 Volts (input from ignition switch) |
| C | Pink (PNK) | IC Control Signal (output to ignition coil) |
| CONNECTOR 2 | ||
|---|---|---|
| Terminal | Wire | Description |
| B | Tan with black stripe (TAN/BLK) | 5 Volts (input from ECM above 400 RPM). |
| E | White (WHT) | ICM control signal (input from ECM above 400 RPM). |
| G | Black with red stripe (BLK/RED) or red with black stripe (RED/BLK) | Ground. |
| R | Purple with white stripe (PPL/WHT) | Fuel control circuit. |
| CONNECTOR 3 | ||
|---|---|---|
| Terminal | Wire | Description |
| N | Yellow (YEL) | Pickup coil signal. |
| P | Green (GRN) | Pickup coil signal. |
Where To Buy The Ignition Control Module And Save
The following links will help you comparison shop for the AC Delco and after-market ICM and distributor pickup coil:
- AC Delco - D1960A Ignition Control Module (at: amazon.com).
- Standard Motor Products - LX339 Ignition Control Module (at: amazon.com).
What Tools Do I Need To Test The ICM And Distributor Pickup Coil?
You don't need expensive diagnostic tools to test the ICM or the distributor pickup coil. The two most important tools you'll need are:
- A multimeter.
- An LED light.
You'll also needs some basic hand tools but nothing more. If you don't have a multimeter or need to upgrade yours, check out my recommendation here: Buying A Digital Multimeter For Automotive Diagnostic Testing.
TEST 1: Making Sure The ICM Is Getting 12 Volts
IMPORTANT: If the ignition coil is sparking, the ICM and pickup coil are working properly at this time. You can find the ignition coil test here: How To Test The Ignition Coil (1987-1993 2.5L Chevrolet S10 Pickup, GMC S15 Pickup, GMC Sonoma).
The first thing we're going to do is make sure the ignition control module (ICM) is getting 10 to 12 Volts.
The ICM gets these 12 Volts on the pink (PNK) wire of the 2-wire ICM connector labeled connector 1 (see figure above).
IMPORTANT: The battery must be fully charged for all tests.
Let's get testing:
- 1
Place the multimeter in Volts DC mode.
Don't have a digital multimeter? Need to buy one? Click here to see my recommendations: Buying A Digital Multimeter For Automotive Diagnostic Testing. - 2
Disconnect the ignition module two-wire connector (see illustration above).
- 3
With the red multimeter test lead probe the pink (PNK) wire of the ignition module two-wire connector.
NOTE: You can probe the front of the female terminal as long as you're careful not to damage it with the multimeter probe. - 4
Connect the black multimeter test lead to the battery negative (-) terminal.
- 5
Turn the key ON with the engine OFF.
- 6
You should see 10 to 12 Volts on the multimeter.
Let's take a look at what your test results mean:
CASE 1: 10 to 12 Volts are present in the PNK wire. This is the correct and expected test result.
The next step is to check if the ignition module is generating a trigger signal (IC control signal) for the ignition coil. Go to: TEST 2: Testing The Ignition Coil Control Signal.
CASE 2: 10 to 12 Volts ARE NOT present in the PNK wire. Without this voltage the ignition control module nor the ignition coil will work.
Your next step is to find out why this voltage is missing and resolve it. Resolving this power issue should solve your engine's no-start problem.
