Hey guys, my check engine light came on, and the code that came up is for the Crankshaft Position Sensor. Is there any reason that code gets tripped aside from the sensor being bad and needing replaced? I guess I'm wondering if any subtle problem with the crankshaft itself could cause an odd signal through that sensor and cause the code to come up. I'm trying to ascertain the origin of a noise that is the subject of another thread; it seems kind like an odd coincidence that the noise might be coming from the crankshaft, and then this sensor code gets tripped. Thanks for any thoughts.

 

What is the *actual* fault code?

 

Sorry, I don't have the number. I had them use their scanner at the autoparts store. I just have the words the guy read off the thing. I can get the number tomorrow if that would help.

 

Yes, it is*important*, otherwise, it wouldn't have been requested. Generic descriptions of fault codes are generally useless.

 

OK, so the fault code is P0340.

Any help is much appreciated.

 

You see the code is important.
If it is 340, it's not the crank sensor but the camshaft sensor.
If it was the crank sensor the motor would not run at all.
The cam sensor times the fuel injection.
The crank sensor is the reference everything else is keyed from though the PCM.
Good luck.

 

Just for the record, I never once said I thought the number wasn't important. All i said was I would go get the number if you guys thought it would help. I'm just here trying to learn stuff and fix my truck. I really do appreciate your guys' help. Please don't anybody take an innocuous remark the wrong way. I've been nothing but kind and respectful to everybody here.

Bluegrass, thank you for your thoughts. That really clear it up. The fact that the truck was running, and I thought it was the crankshaft sensor, it made me wonder if a problem with the crankshaft itself had caused the fault, and not the sensor itself. So it makes perfect sense it turns out to be another sensor entirely.

 

I suspect it's a timing chain and/or tensioner problem.

 

Takeda, is that what most commonly causes that fault? Are there other less common things as well? Is there any way of knowing more specifically what it is before tearing into stuff to physically examine the parts? I have a noise that might be coming from the engine's bottom end; no odd sounds or anything from up higher.

 

A P0340 on a '99 4.6 isn't a very common problem. Most likely, it will be due to a bad cam sensor, its wiring/connector, or a PCM concern.

Might be a transient or intermittent. Try resetting it and see if it comes back.

 

I've had the battery disconnected several times lately for extended periods to do work to the truck. That was when the light first started coming on, after I fired the truck back up. After subsequent durations of the same thing, the light now keeps coming back on. It takes it maybe five minutes to come on. The work I'd been doing to the truck was brake work mostly. I also cleaned out the throttle body. Is disconnecting the battery like that sufficient to clear that code and to get everything to properly reset, or is that part of the problem do you think? And should I use a scanner to clear it instead?

 

If you disconnect the negative battery cable, and touch it to the positive battery cable, this should be enough to discharge the decoupling capacitors on the un-switched 12V in the PCM. You can also turn the headlights on before disconnecting the negative battery cable, and this will accomplish the same thing. This eliminates the long wait to reset the PCM when just disconnecting the negative battery cable.

When you were working on your truck, was there any arc-welding done? This can damage electronic components, like PCM, GEM, etc. .....

 

Removing power to the PCM each time completely reboots the program back to is base settings as new.
All tables that learn drive cycles on average are reset back, to learn again.
This may take several drive cycles for most and several weeks for the fuel system to be fully tested.
The only difference between a power down and a clear is the tables are cleared on a power down and diagnostics are always done, where the tables are left in tact, on a clear, and diagnostics are done.
With a power down, it only takes a minute or less to clear the tables and codes.
With a clear, only the history and any codes are reset.
No need for long time power downs just to reboot the PCM.
If the 340 only, keeps coming back, address that fault only because the PCM is detecting a fault with it or the circuit it works on.
These systems are precise. Do not stray to other things and thoughts not related.
Good luck.

 

The CEL does keep returning then.

Let me back up a little. There actually was a noise I thought was coming from the passenger side valve train. So I replaced several lifters in the area where it seemed to be loudest, thinking it might be a collapsed lifter. It didn't go away. My neighbor who is an old mechanic said he thought it sounded like the injectors. Incidentally, he is a huge Chevy guy and hates Ford, so we don't work together as much as we might. I get sick of listening to him. But I took his word for it about the injectors, although it still seems kind of strange to me, because the injectors on the driver's side do not sound like that. You can hear them, but it's not nearly as loud and the sound quality is different, and if you put a stethoscope to the driver's side valve cover, you don't hear anything. On the passenger side, you do.

I also did the plugs, but foolishly replaced them with Autolites at first, because I didn't know not to, and that's what was already in the truck. The truck got driven maybe twice that way and started to misfire. So I did some Motorcraft plugs, wires, and coils. I had access to a loaner vehicle, so I decided to redo the brake lines too, as they were rotten as hell. The truck sat with the battery disconnected for several weeks as I chipped away on stuff. No welding was involved. When I fired it back up is when the CEL began coming on.

 

if your plug gaps are out of spec, you will get all kinds of misfire