Symptom: No Start, No Spark or Injector Pulse.

Theory: This Tech Tip will work on the above listed cars but is not vehicle-specific in order to broaden the coverage. All you need in addition to the information here is a wiring diagram for your particular vehicle. These systems use cam and crank sensors that report to the PCM, which then controls a power-transistor, ignition-module or the coil directly. Again, a quick check of a wiring diagram will show you exactly what your vehicle has.

The Test: The best way to diagnose this system is with a Scanner and Vantage or Modis. Once you have determined that you are missing spark or injector pulse, hook up the Scanner or Modis and select “ATM Tests” from the “Functional” menu. Now, you can command the PCM to fire the coil(s) and injectors. By doing this, you confirm that the PCM is functioning. If you can’t get the PCM to do anything, use the wiring diagram to check power and ground inputs. We’ll also need to check signals from the cam & crank sensors, which is covered at the end of this section. If you do not get spark but the PCM operates the injectors, we’ll have to check ignition primary wiring, module and coil(s). Make sure you have battery voltage present at the positive side of the coil(s) with the engine cranking. If there’s no voltage, diagnose using the wiring diagram. If voltage is present, use the Vantage or Modis to check the signal from the PCM to either the ignition module or negative side of the coil. If the signal is present, you are looking at a bad module or coil. If there is no signal but you had injector pulse in the first test, the PCM may be defective. Do not replace the PCM without checking the wiring and coil(s) to prevent a repeat failure. If you are missing both ignition primary and injector pulse, there still may be a problem with the PCM, but we need to check the cam and crank sensor signals first.

There are two ways to do this, one is quick and the other is precise. The quick way is to watch cam & crank status on the Scanner or Modis with the engine cranking over. They should both read “YES” if they’re producing a signal. A constant or intermittent “NO” indicates a need for further testing using the Vantage or Modis, which is the precise way of checking the sensors. Using the wiring diagram, identify the signal wire at the cam and crank sensors. Each sensor should produce a square-wave pattern, although the crank sensor signal will be much closer together on the screen. If you want to check frequency from the sensors, a general rule of thumb is 20 to 60 hertz for the crank sensor and 2 to 30 hertz for the cam sensor. These specs are with the engine cranking over.

The Fix: Replace any parts found to be bad during above testing. Remember, if you end up replacing the PCM or ignition module, be sure to check for a defective coil so you don’t kill the new part. If you need to replace a cam or crank sensor that’s adjustable, you can make an easy spacer from a matchbook or the back of a note pad. Just cut a circle out of the cardboard the same size as the bottom of the sensor. Glue this to the bottom of the sensor with rubber cement. Install the sensor, pushing it in until it bottoms out. When the engine is started, the cardboard spacer will be rubbed off, leaving the correct sensor air-gap.