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If a crank or cam sensor fails, the engine will not start. Both of these sensor circuits can be checked with a voltmeter or lab scope.
If the sensors are receiving the correct amount of voltage and have good low-resistance ground circuits, their output should be a pulsing digital signal or voltmeter reading while the engine is cranking.
If any of these conditions do not exist, the circuit needs to be repaired or the sensor needs to be replaced. When the engine fails to start, follow these steps:
Check for fault codes 11 and 43.
Code 11, "Ignition Reference Signal," could be caused by a defective camshaft reference signal or crankshaft timing sensor signal.
Code 43 is caused by low primary current in coil number 1, 2 or 3.
With the engine cranking, check the voltage from the orange wire to ground on the crankshaft timing sensor and the camshaft reference sensor.
Crankshaft timing and camshaft reference sensor terminals.
Over 7V is satisfactory.
If the voltage is less than specified, repeat the test with the voltmeter connected from PCM (powertrain control module) terminal 7 to ground.
If the voltage is satisfactory at terminal 7 but low at the sensor orange wire, repair the open circuit or high resistance in the orange wire.
If the voltage is low at terminal 7, the PCM may need replacement.
Be sure 12V are supplied to the PCM terminal 3 with the ignition switch off or on, and 12 V must be supplied to PCM terminal 9 with the ignition switch on.
Check PCM ground connections on terminals 11 and 12 before PCM replacement.
With the ignition switch on, check the voltage drop across the ground circuit (black/light blue wire) on the crankshaft timing sensor and the camshaft reference sensor.
A reading below 0.2V is satisfactory.
NOTE
When using a digital voltmeter to check a crankshaft or camshaft sensor signal, crank the engine a very small amount at a time and observe the voltmeter. The voltmeter reading should cycle from almost 0 volts to a highter voltage of about 5 volts. Since digital voltmeters do not react instantly, it is difficult to see the change in voltmeter reading if the engine is cranked continually.
If the readings in the previous two steps are satisfactory, connect a lab scope or digital voltmeter from the gray/black wire on the crankshaft timing sensor and the tan/yellow wire on the camshaft reference sensor to ground.
When the engine is cranking, a digital pattern should be displayed or the voltmeter should cycle between 0 and 5 volts.
If the voltage does not cycle, sensor replacement is required.
Each sensor voltage signal should cycle from low voltage to high voltage as the engine is cranked.
A no-start condition can occur if the PCM "locks up."
In step 2 above, if 0 volts is indicated the PCM may be faulty or it may be locked up.
If the PCM is locked up it will not store a fault code for the reason.
Basically, the PCM will lock up when it goes into a safeguard routine if the 9-volt or 5-volt reference voltage shorts to ground. This shuts down the PCM to protect it. Since it shuts down, no DTCs (Diagnostic trouble code) are stored.
The engine will not start as long as the ground is present. An intermittent ground will cause the engine to stop running.
Attempting to restart the engine without cycling the ignition switch to the full LOCK position will not start the engine, even if the ground is lifted.
Cycle the ignition switch to the LOCK position and wait about 5 to 10 seconds.
If the ground is lifted, the PCM will reset and the engine will start and run until the ground occurs again.
On 1996 and new SBEC III and JTEC engine controllers, there are two 5-volt reference signals. The sensors that require 5 volts are separated, thus If this signal shorts to ground the engine will still stop running, but for the first time a DTC can be set.
Also note, if the 9-volt reference voltage is opened, there will be no DTC stored for the crankshaft or camshaft positions sensors. With an open circuit the PCM cannot tell if the engine is cranking or not. The diagnostic routing does not begin until the PCM senses engine cranking.
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