DTC 18

Code 18 Diagnostic Chart:

Ignition System Circuit Diagram (Type II):

CIRCUIT DESCRIPTION:
During cranking, the ignition module monitors the dual crank sensor sync signal. The sync signal is used to determine the correct cylinder pair to spark first. After the sync signal has been processed by the ignition module it sends a fuel control reference pulse to the PCM. When the PCM receives this pulse it will command all six injectors to open for a (priming) shot of fuel in all cylinders. After the priming, the injectors are left "OFF" for the next six fuel control reference pulses (two crankshaft revolutions) from the ignition module. This allows each cylinder a chance to use the fuel from the (priming) shot. During this waiting period, a cam pulse will have been received by the PCM. Now the PCM begins to operate the injectors sequentially, based on true camshaft position.

With the engine running, the PCM monitors the cam and fuel control reference pulses. It expects to see six fuel control pulses for each cam pulse. If the sequence of pulses is incorrect for ten occurances, a code 18 is set, indicating a problem with the cam signal or fuel control signal.

TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart.
1. Determines if conditions necessary for a code 18 exist.
2. If 5 volts is not present at PCM harness connector "BA12", the cam sensor may be interfacing with the magnet in the camshaft sprocket. Turning the engine a few degrees should change this by moving the magnet farther away from the sensor.
3. If a failure is induced in the fuel control reference circuit, a change in the voltage reading should occur when the connection is opened (poor connection or broken wire.)

NOTE: If code 41 is stored along with code 18, see code 41 diagnostic chart first.

DIAGNOSTIC AIDS
Code 18 indicates an intermittent fault and may not set immediately or under all conditions. Customer comments about the kind of symptoms experienced may help isolate the cause of the condition. A poor connection or fault in the cam sensor circuits 630, 633, 644, or 645, or a faulty cam sensor may cause the PCM to re-initialize injector sequence when the fault occurs, possibly causeing a stumble or miss. A poor connection or fault in the fuel control circuit 430, crank sensor circuits 643, 644, or 645, the 18X portion of the crank sensor or bent/missing vanes on the harmonic balancer interrupter rings will cause the PCM to stop pulsing the injectors when the fault occurs. This may be noticed as an intermittent stumble or stall.