The infamous P0340: Camshaft Position Sensor Fault but with no symptoms of one

[dictoresno]

After driving 40 miles to work, I stopped for coffee. When I restarted the car, CEL tripped. Used the access port to pull the P0340 code, Camshaft Position Sensor 'A' Circuit Signal Fault Bank 1 Or Single Sensor

Car drives fine, no stuttering, loss of power and starts right up without issue. Cleared the code, came right back. I purchased a new sensor, but in the mean time I read a lot about it and some people state they had phantom codes. Most of the threads were old, with no resolution. Has anything developed more over the years regarding this issue? Since I don't have any obvious signs of malfunction, can i drive it until monday when the sensor delivers?

2002 WRX, full engine rebuild about 2 years ago (new valves, seals, some lines, new timing belt kit with pulleys and no issues since)

Also, FSM shows only one sensor, front drivers side next to dipstick. Other online exploded parts diagrams show 2 or 3 potentially. Is it just the one or what?

[quazimoto]

Just the one. If the car is driving fine then just drive it. Its not going to hurt anything. The FSM also has a full diagnostic guide to most of the DTC's. My guess is if the sensor isn't bad it could be corroded terminals or a fault in one of the wires.

[mrsaturn7085]

Electrical faults like this will trigger a code before it causes an issue - it's exactly what the OBD system is for. Replace the sensor now, or wait a while and disable the DTC. Either way, it's on it's way out.

[dictoresno]

Originally Posted by mrsaturn7085

Electrical faults like this will trigger a code before it causes an issue - it's exactly what the OBD system is for. Replace the sensor now, or wait a while and disable the DTC. Either way, it's on it's way out.

ok thanks, new sensor will be here tomorrow. just wanna know if i will be able to drive the car in the mean time or not.

[CosmoTheCat]

My OBS threw that code.

Because the timing belt snapped.

[dictoresno]

My belt should be good. New kit installed 25,000 miles ago

[CosmoTheCat]

I was just pointing out that the code doesn't always mean the sensor is bad. You'd know it if your belt was broken, it wouldn't run.

[dictoresno]

well the sensor came today. popped the battery out, swapped the sensor in about 10 mins. initial startup, car sputtered a bit at first but eventually idled fine. code stayed on and came right back after resetting the ECU. decided to take the car for a quick drive, drove just as good as it did before. once i got home after a quick 3 mile ride, i decided to erase the code again. it was only then, the light decided to stay off. so far so good. guess it needed a drive cycle before it could verify pulses were all correct.

[HoosierBuddy]

I wonder if it might have had already logged a "pending" code. My code reader shows both active and pending categories. That being said, I don't know how/when a code moves from pending to DTC.

Phil

[dictoresno]

Ok well the code just came back again. This is getting annoying.

[dictoresno]

Ok cleared the code and now it's OFF again. Spoke to my contact at the local dealer, he sent me the diagnostic info for checking the wiring if this doesn't work. I'm praying the "pending previous code" theory was the cause for it to come back. Let's see what happens.

[dictoresno]

Well I reset the light last night. Started the car again, it stayed off. Left for work today and it was off all drive to work and after filling up gas. Then came back on upon startup after leaving a 7-11. I'm definitely puzzled.

I deleted the code and it will go away again. So weird.

[CosmoTheCat]

Originally Posted by dictoresno

Also, FSM shows only one sensor, front drivers side next to dipstick. Other online exploded parts diagrams show 2 or 3 potentially. Is it just the one or what?

There will be multiple cam sensors on vehicles with variable cam timing.


How's the area where your cam sensor mounts? Bent or deformed at all? How's your intake cam end play? Have you verified your timing yet? Have you checked wire continuity/resistance and pin tension yet?

You can try shimming the cam sensor out a hair, put a washer or similar between the sensor and housing. Clear memory and see if you can start/drive it.

[dictoresno]

I've replaced the sensor, which at first gets rid of the DTC. every few startups, the code will trigger again randomly after being deleted. sometimes it will trigger right away, other times will take a few start/stop engine cycles to trigger. it will only trigger during startup, which makes me thing its the in the first 2 seconds where the reading isn't correct but the ECU, or its expected signal isn't there. the only weird thing is everything i read says common symptoms associated with this code is no start or rough start/idle and loss of power. i have none of these issues. i was just able to delete the code and get it to stay off for 3 engine start/stop cycles. i ordered a multimeter so i can check for resistance. i have the DTC troubleshooting guide from the dealer. i can post it up if someone wants to read it over.

[CosmoTheCat]

I wouldn't eliminate it as a possibility, but the odds of a brand new out of the box sensor having the same problem is low.

You could have an air gap issue (read: camshaft walking fore/aft or housing deformed where the sensor bolts)
You could have an issue with the cam pulley.
You could have a loose electrical connection somewhere - loose pin, pin backing out of connector, etc.

[dictoresno]

Originally Posted by CosmoTheCat

I wouldn't eliminate it as a possibility, but the odds of a brand new out of the box sensor having the same problem is low.

You could have an air gap issue (read: camshaft walking fore/aft or housing deformed where the sensor bolts)
You could have an issue with the cam pulley.
You could have a loose electrical connection somewhere - loose pin, pin backing out of connector, etc.

i rebuilt the engine myself two years ago, I'm willing to bet and hope #1 and 2 are not it. electrical connection bad or backing out or shorting seems more likely. you would figure though, the short to electrical issue would trigger the DTC everytime. however, its intermittent and only on startup.

[CosmoTheCat]

What happens on startup that doesn't while driving down the road, typically?

Do a wiggle test - with the CEL off, engine running, wiggle electrical connections and the harness and see if you can get the CEL to trigger.

[dictoresno]

Originally Posted by CosmoTheCat

What happens on startup that doesn't while driving down the road, typically?

Do a wiggle test - with the CEL off, engine running, wiggle electrical connections and the harness and see if you can get the CEL to trigger.

during startup, the cam and crank sensors are read by the ECU to determine timing, fuel and other things needed for startup. i think this is when the DTC for the cam sensor will be tripped, and not while driving. to support this, I've only had it trip in the first 3 seconds of engine start, never while driving.

good idea on the wiggle test, ill try that tomorrow.

[dictoresno]

ok so today, i had 3 start/stop drive cycles. upon the 3 engine restarts, the DTC was not triggered at all. and this was after sitting overnight after deleting it the last time. last night when i deleted the code, i restarted the engine 3 times and it still didn't trigger. so I'm hoping that its finally gone now.

[CosmoTheCat]

The cam and crank sensors are monitored constantly. The code pops when an error is detected.

When you start the motor, it typically moves around a lot more than while driving. I'd be focusing on anywhere the wires might be chafed, and closely inspecting all joints.

[dictoresno]

well went a few days with no issue, but today while driving on the highway the CEL came on again. a few miles later the car sputtered a bit but instantly back to normal. drove fine, starts fine. I'm able to delete the code and have it stay off for the time being, but it will randomly return. before i replaced the sensor, it would always come back instantly. I'm waiting for a chance (working nonstop) to check the plug with a multimeter. i have a feeling theres something killing the signal, but the car driving fine even with the fault code keeps confusing me. tried the wiggle the wires test today and moved some around, didn't see anything obviously wrong with any. ill keep checking. but I'm about done trying to deal with it and considering letting the dealer look at it. i don't have the time between work hours (doing doubles) and a small baby at home to keep fumbling with it.

[dictoresno]

Ok so today I was running for like two days without issue. Then, turned my AC on and within minutes, the light kicked on and the car got a little sputtery. Turn the AC off, the issue went away. Wonder if the AC compressor is causing drag on the system and creating the error.

[dictoresno]

ok so i finally took the car into the dealer since i gave up on it.

they looked at it for a few hours and concluded the following:

1.) new and old sensors seem to be working fine (was never the sensor to begin with)
2.) wiring harness from sensor to main harness is fine
3.) wiring harness from main harness to ECU is fine

They are getting another senior tech tomorrow to look into the ECU as a possible issue. Stumped all 3 techs working on it today.

[CosmoTheCat]

Put a scope on it, monitor the cam sensor while operating normally, then compare that to the signal when the AC compressor engages. It very well could be a compressor issue.

edit: And have the dealer do that BEFORE you spend hundreds of dollars on an ECU that most likely won't fix the problem.

[dictoresno]

Dealer called me today. They said nothing appears to be wrong. They have it narrowed down to a possible ECU issue and want me to reflash my tune to see if that helps. Other than that, they are out of ideas.