DTC 18

Engine Cranks But Won't Run Circuit:

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 one priming shot of fuel in all cylinders. After the priming, the injectors are left "OFF" for the next six fuel control reference pulses from the ignition module (two crankshaft revolutions). 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 references pulses it receives and expects to see six fuel control pulses for each cam pulse. If the sequence of these pulses is not correct for 10 occurrences Code 18 will set, indicating an intermittent problem with the cam signal or fuel control signal.

Code 18 Diagnostic Chart:

Test Description:
Number(s) below refer to circled number(s) on the diagnostic chart.

1. Determines if conditions necessary to set Code 18 exist.

2. If 5 volts are not present at PCM harness connector terminal "BA12", the cam sensor may be interfacing with the magnet in the camshaft sprocket. Bumping the starter should correct this condition.

3. If a failure is induced in the fuel control reference circuit, the 5 volts on the circuit should change when the faulty wiring or connection is manipulated.


NOTE: If Code 41 is set along with Code 18, use Code 41 chart for diagnosis.


Diagnostic Aids:
Code 18 indicates an intermittent fault and may not set immediately or under all conditions. Customer comments of symptom experienced may help isolate the cause of the condition. A poor connection or fault in the cam sensor CKTs 630, 633, 644 or 645 or a faulty cam sensor may cause the PCM to re-initialize injector sequence when the fault occurs, causing a possible stumble or miss. A poor connection or fault in the fuel control CKT 430, crank sensor CKTs 643, 644 or 645, the 18X portion of the crank sensor or bent or missing vanes on the harmonic balancer interrupter rings will cause the PCM to stop pulsing the injectors when the fault occurs, causing an intermittent stumble or stall.