Hi guys. Crank sensor has to be good because that's what the engine is running on. Beginning around 2000 / 2002, the systems were changed to allow the engine to run on just one sensor. Before that the Engine Computer had to see signals from both sensors before it would turn on the automatic shutdown relay which powers the ignition coil(s), injectors, fuel pump or pump relay, and other stuff.
You have two possibilities. The cam sensor is shorted or the valve timing is off. If the cam sensor is shorted, it will kill the 5.0 volt supply for both the cam and crank sensors. Unplugging the shorted sensor will restore the 5.0 volts to the good one but since the computer shuts the power supply down to protect it, you have to turn the ignition switch off first, then back on to reset it. When the power supply is shut down by the computer, you will see "no" listed for both sensors on a scanner that can display live data. If you see "present" listed for one sensor, neither one is shorted but the one listed as "no" is either defective or has a wiring problem.
If the timing is off, there are again two possibilities if you have the single overhead cam engine. About half of the time you're going to find the timing belt has jumped one tooth. At that point the computer will detect the mismatched signals, set a diagnostic fault code "cam and crank sync", and turn on the Check Engine light. The engine will still run but it will be down on power.
If the timing belt jumps two teeth, the computer will shut the engine down to protect it from serious damage. It does that by failing to turn on the automatic shutdown (ASD) relay. That kills the injectors, ignition coils, and fuel pump. By forcing the engine to run when you unplug the cam sensor, it provides a valuable clue, but you risk doing expensive valve damage. When the timing belt jumps three teeth, the open valves will be hit by the pistons as they coast to a stop. Those bent valves can only be repaired by removing the cylinder head to replace them. The additional clue here is at two teeth off, the engine will be running very poorly if it hasn't shut down yet. If it runs fine when you disconnect the cam sensor, most likely it's a sensor problem, not a timing belt problem. If the engine runs poorly with the cam sensor unplugged, it's not wise to force it to do so to get it home or to a shop because when the timing belt jumps teeth, it's usually because those teeth are being sheared off from an entire section of the belt. That means it won't be long before that valve damage occurs; perhaps even in the next few hundred yards.
The second timing issue has exactly the same result, symptoms, and clues, except the timing belt will be in good shape and correctly adjusted. The key between the camshaft and sprocket shears off and over time the resistance of turning the camshaft causes the sprocket to turn on the cam. That makes the camshaft timing late just as if the belt had jumped a tooth. Since the cam sensor is at the end of the camshaft opposite the sprocket, the pulses it develops show up late compared to the crankshaft sensor's pulses. All the computer knows is the valve timing is late and damage to them could occur soon. It doesn't know, (or care), if that is because the cam and sprocket are late due to a jumped belt, or the cam is late because it is turned on the sprocket.
At the mileage you listed you can justify installing a new timing belt. If the old belt is off one or two teeth, the valves should be okay yet. This is the perfect opportunity to install a new key between the cam and sprocket. Be aware the pressure from the valve springs is going to make the camshaft want to turn a little when you remove the belt. A valve might hit a piston but it won't be damaged if you don't put excessive pressure on it. If you start with the crankshaft at TDC, the cam won't turn very far and won't take much effort to move it back to the correct setting when you put the new belt on. Install the new belt and time it correctly by only turning the crank and the cam sprocket by hand.
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Wednesday, December 28th, 2011 AT 10:12 PM