OBDII weirdness

Steve777 · **Joined:** Fri Oct 16, 2015 11:31 pm **Posts:** 279

Drove the CRD to the airport to fly out to a wedding. When we came back it started just fine but I noticed the engine light was on. Pulled the codes with my ELM27 reader and Torque Lite and saw a P0340 code (cam position sensor), and I cleared it to see if it would come back. Tried reading codes after the clear and it found none, OK. Started the engine and the engine light was still on, tried to read codes again but it still found none. Tried read codes several times but it read none???

This behavior seems odd, if the engine light is still on, I would expect there are stored codes to read. Any thoughts on this? Should I order up a cam sensor or does this sound like something else is going on here?

Steve777 · **Joined:** Fri Oct 16, 2015 11:31 pm **Posts:** 279

A small update. Went out again 15 mins later and now the P0340 was back again on Torque Lite. Hmmm, perhaps it takes a couple of key on-off cycles for the codes to get thru. Anyway, cleared it again and this time it seems to have stayed away; at least the engine lite stayed off. I will see how it holds up.

Seems that these cam sensors are a fairly common failure mode. I'll check the wiring and clean the contacts once the weather improves a bit. But unless there is a wiring issue I can find/correct I am assuming it is prudent to just go ahead and replace this, before it leaves me stranded somewhere.

APC9199 · **Posted:** Tue Mar 20, 2018 8:55 pm

I would just order one. They are not terribly expensive and it WILL leave you stranded somewhere, likely at the least opportune time. If you change it out and the problem persists, hold on to the old one as a backup, maybe.

Steve777 · **Joined:** Fri Oct 16, 2015 11:31 pm **Posts:** 279

Thanks APC. I did check the wires at the connector and they all looked fine, so I ordered and put in a new MOPAR cam sensor. Cleared the P0340 code and drove it around for a few days (130 miles or so) no problems. Thought I had this problem licked. But today the engine light come back on and when I pulled the codes it was P0340 again.

So, when it's daylight again I will check the wires, connector and new sensor, but I suspect those are all just fine. Possible a break somewhere in the harness, or I was thinking back to last spring when I had an injector code and it turned out to be goo in the connector at the ECU. Perhaps there is goo in more of those pins causing this problem...

Anyway, thought I ask again, any other possible causes of this problem? BTW the jeep runs fine when the code comes up, so if it is a bad connection somewhere I'm guessing it is fairly intermittent, otherwise seems like the engine would die on me. And I don't think it's related but this last tank of fuel gave me lousy mileage???

Thoughts anyone?

GordnadoCRD · **Posted:** Thu Mar 29, 2018 6:15 am

The wires for the CMP sensor are ones that pass through the known possible pinch point behind the fuel filter bracket.

Recommend looking up the CMP pin check troubleshooting in the factory service manual between the sensor connector and the ECM connector (Opens, grounds, shorts, and resistance)
If all the wires are good, it may be loose pin sockets in the connector it's self, and need to be changed out.

Steve777 · **Joined:** Fri Oct 16, 2015 11:31 pm **Posts:** 279

Thanks again GordnadoCRD.

Yeah I pulled the fuel filter & bracket and checked the wires under that spot about 1 year ago when I was digging into the injector issue. The wires were fine, and I wrapped them in some additional tape and foam when I put things back together there, so likely not there (but if my other efforts don't clear this up I will look there again).

I did pull the top (C1) ECU connector and checked the 3 wires from the cam sensor. Pulled each of the pins out of the connector. Each one was coated in the same goo as I found on the injector wire connectors a year ago! One was really covered in it. This is not just someone pushing some silicone compound into the connector when he grabbed it with dirty hands, the goo is way back on these contacts. I think it comes from sloppy assembly of the harness back at the factory (or contract house). Anyhow I cleaned these guys up, gave everything a wipe with WD40, and put it all back together. Drove around the block a couple of times and so far the code has stayed away. Unfortunately it can take a while for the code/engine light to reappear, so I will need to keep an eye out for a while, and don't do any long trips with the CRD until it seems this problem has really been fixed.

On some sunny day in the future, I need to pull that C1 ECU connector again, pull each of the wires in there and clean them out. Not fun, but it seems likely there are more surprises that will likely be coming from this goo if I don't.

GordnadoCRD · **Posted:** Thu Mar 29, 2018 9:56 pm

It's possible, that stuff, (at one time) could have been di-electric grease, intended to keep moisture / salt / corrosion out. (and subsequent partial shorting)
Either way, it is a good mod to make, once removed and cleaned. In certain environments, it becomes saturated with the stuff it's keeping out, and needs to be periodically cleaned and re-applied, or it becomes conductive it's self.

Steve777 · **Joined:** Fri Oct 16, 2015 11:31 pm **Posts:** 279

Yeah Gord, could have been the intent (dielectric grease). But at this point, on my CRD, it seems to have combined with dirt/dust to cause problems. Definitely the sole issue on my Injector code about 1 year ago, and likely partially responsible for the cam position sensor problem now (although I am not at the end of this one yet).

So weather and schedule finally aligned, and I got a chance to spend a bit more time on this. The clean up of the CPS pins at the ECU seemed to help; I can now drive 2-10 miles before the P0340 code and engine lite come back, but that obviously did not solve it. I've checked the harness behind the fuel filter and no signs of any wear or pressing on any wires. I looked at the connector at the sensor and from what little I could see all seemed fine. I checked the resistance between the ECU connector pins and the sensor connector pins, again all seemed fine, no shorts, no opens, no high resistance. Hey, when I was putting everything back on the last time, I intentionally left the CPS sensor connector disconnected at first just to see what would happen. I was expecting a nostart since everyone says the CPS is critical to the engine running; but it started and idled just fine, and I even rev'd it up a few times with no issues (or course the engine lite and P0340 came back).

So I am puzzled??? No obvious problem here! Here are a few thoughts/questions, hopefully some of the experts here can shed some light on what might be going on:

1. What exactly triggers a P0340 code? Could it be fairly intermittent? Is it just no signal, or does the ECU monitor proper current to the sensor too?

2. Why did my engine run with the sensor unplugged? Shouldn't that have kept the engine from starting/running? And how long does the error have to be present before it kills the engine?

3. What are the chances that my new CPS is defective (it's a new Mopar one)? Having replaced a bad sensor with another new but bad one could certainly explain all this...

4. Any chance that the camshaft is worn or out of position and that would cause a bad signal from the sensor? (I assume a bad camshaft would be making a lot of noise and other signs that something is wrong, which it isn't. But hey I am trying not to leave any stone unturned here.)

5. Glitch in the ECU, some other problem and it is throwing the wrong code? A long shot, I put a set of bits from here on there to take out the ERG and it has been working just fine til now, but hey...

Any thoughts or ideas would be welcome.

TIA

joe_ · **Posted:** Sat Apr 07, 2018 10:01 pm

Steve777 wrote:

3. What are the chances that my new CPS is defective (it's a new Mopar one)? Having replaced a bad sensor with another new but bad one could certainly explain all this...

Was thinking about this a bit, and I remember there being an o-ring on the sensor to seal against the valve cover. Is it possible the old o-ring stayed in the valve cover when you removed the old sensor, and now you have two o-rings in there (therefore preventing the new sensor from fully seating in place)?

Steve777 · **Joined:** Fri Oct 16, 2015 11:31 pm **Posts:** 279

Good thought Joe, but don't think so. First I made sure the Oring was on the old one when it came out (thought I was going to have to reuse it). And when I put the new one in, I rotated it and checked that it was flush with the valve cover/manifold before aligning the hole and putting the screw in. So unfortunately probably not.

GordnadoCRD · **Posted:** Sun Apr 08, 2018 4:31 am

If I'm following correctly, can I assume that by CPS you are referring to CMP (camshaft position) sensor, and not CKP (crankshaft position) sensor?

When you pulled the ECM connector, did you check for low ohm shorts and resistance specs between the wires?

Steve777 · **Joined:** Fri Oct 16, 2015 11:31 pm **Posts:** 279

Opps, wrong abbreviation, yes CMP camshaft position sensor.

I did check briefly for shorts between the wires, but was mostly looking for an open in one of the wires (tugging and pulling on the wires to see if I could cause it to open up). I did not check to see if any of these wires were shorted to ground at all. Have to go back and do that.

Steve777 · **Joined:** Fri Oct 16, 2015 11:31 pm **Posts:** 279

Well I think the mystery is solved... I got a defective new sensor!!

I did check the wiring one more time, no shorts or opens, all wires low resistance from the ECU to the sensor. I went to the FSM and went thru their debug procedure for P0340 (they have two of them actually), as best I could without a scope or a DRBIII; everything checked out again (at least the stuff I could check). Just for grins I replaced the new sensor with an old one from the CRD which I am replacing the head on, it has 140K miles on it but wasn't throwing any camshaft codes when I pulled the head. Voila, problem fixed. With the new sensor it used to throw a P0340 after ~5 miles or so, just enough to warm up the engine. With this old sensor in there I've gone ~100 miles with numerous starts, run up to full temp and drive, and then park and do it again with no problems.

A defective new sensor is the last thing I would have thought it could be. Now it will be interesting to see if the mopar place I bought this sensor from will replace it.

OBDII weirdness

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