Eh? P0624 Fuel Cap Lamp Control Circuit

BiodieselJeep.com · **Posted:** Fri Sep 15, 2006 8:59 pm

What the heck is that? My wife said she had the Firebolt light come on today on the way home (Electronic Tranny Control, right?). When I got in the car, though, all there was was a CEL, did the key trick and pulled this weird code. Found it on a G site: P0624 Fuel Cap Lamp Control Circuit? I don't think that there is a lamp in my fuel port...nor does my Sport model have a fuel cap monitor (I don't think).

Wah?

ps it is raining like I should build an ark. Maybe its a short?

BiodieselJeep.com · **Posted:** Sun Sep 17, 2006 12:03 am

Now the CEL is off. I would actually prefer it to be on...at least it wouldn't mean that the wiring is wimpy and subject to the whims of weather! A genuine problem that could be fixed with a bolt or something would be better.

DarbyWalters · **Posted:** Sun Sep 17, 2006 8:38 am

If the fuel cap is not tight...it will send a code. If it is them tightened it will eventually go away. Maybe that was it

retmil46 · **Posted:** Sun Sep 17, 2006 11:17 am

DarbyWalters wrote:

If the fuel cap is not tight...it will send a code. If it is them tightened it will eventually go away. Maybe that was it

Uhhh, I hate to call this on one of the august founders of LOST, but that only works on the gassers. Our CRD's have a VENTED fuel tank, so the fuel pump on the front of the engine can suck diesel uphill from the opposite end of the vehicle. Think 80's MB diesel, '04 and earlier Dodge Cummins - essentially the same type of setup as far as fuel supply and return and the tank itself.

From the description of what occurred and the heavy rain part, I'd say the guess of an electrical problem may be spot on - water managed to find it's way inside one of the harness connectors.

As far as it throwing the gasser code for a loose fuel cap, probably a "legacy" code that was carried over in the software and means something else for our diesels. The way DC has kludged the programming for these beasts, I wouldn't be surprised.

DarbyWalters · **Posted:** Sun Sep 17, 2006 12:16 pm

retmil46 wrote:

DarbyWalters wrote:

If the fuel cap is not tight...it will send a code. If it is them tightened it will eventually go away. Maybe that was it

Uhhh, I hate to call this on one of the august founders of L.O.S.T., but that only works on the gassers. Our CRD's have a VENTED fuel tank, so the fuel pump on the front of the engine can suck diesel uphill from the opposite end of the vehicle.

.

I KNOW that we have a mechanical pump that is driven off the engine...it would still not surprise me that DC did not change the sensors and let us know our cap is not tight. :wink:

I know in the past you have posted about the fact that the pump sucks the fuel and a gas cap could not cause starvation. Hence the word "Maybe" in my post...

oldnavy · **Posted:** Sun Sep 17, 2006 1:12 pm

DarbyWalters wrote:

retmil46 wrote:

DarbyWalters wrote:

If the fuel cap is not tight...it will send a code. If it is them tightened it will eventually go away. Maybe that was it

Uhhh, I hate to call this on one of the august founders of L.O.S.T., but that only works on the gassers. Our CRD's have a VENTED fuel tank, so the fuel pump on the front of the engine can suck diesel uphill from the opposite end of the vehicle.

.

I KNOW that we have a mechanical pump that is driven off the engine...it would still not surprise me that DC did not change the sensors and let us know our cap is not tight. :wink:

I know in the past you have posted about the fact that the pump sucks the fuel and a gas cap could not cause starvation. Hence the word "Maybe" in my post...

Easy boys, easy... D/C just left the idot light in place for the gassers and there is no sensor to make it work on the CRD. I fill the CRD all the time with engine running and have never seen the fuel cap warning light come on. Even drove it about 10 miles down the road once when I saw it dangling in the rear view mirror and no idiot light to tell me it was off. :oops:

retmil46 · **Posted:** Tue Sep 19, 2006 12:05 am

Anyhow, we still have the question of what this "gasser" DTC means on our CRD's. Is it just a "ghost" code that was caused by a water induced electrical gremlin, or does it actually indicate an honest-to-god malfunction on the CRD and different than the fuel cap?

oldnavy · **Posted:** Tue Sep 19, 2006 8:20 am

A valid point about what caused the code, most likely the "ghost" code from some type of electrical glich. There should not be another code using the same sensor and fuel cap loose warning dash light for something totally different. When I speak of fuel cap warning light in the dash, I have not seen it on the dash but I seem to remember seeing it in OM booklet.

litton · **Posted:** Tue Sep 19, 2006 10:39 am

Don't mean to get sidetracked, but what is the "key trick" that allows you to retrieve the code?

tks

retmil46 · **Posted:** Tue Sep 19, 2006 11:47 am

Wouldn't know for certain without researching the FSM, but here's a guess as to what caused the code, given DC's penchant for using common parts.

From what I understood of the evap emissions system on my '04 Dakota, the most likely way they were sensing that the fuel cap was loose was not a sensor on the actual cap itself, but from a pressure or vacuum sensor somewhere in the system. If the cap was loose, it wouldn't allow the system to either build up pressure or pull a vacuum on the fuel tank, the sensor would detect this, and the "loose fuel cap" light and code would be thrown based on the lack of pressure/vacuum.

If the CRD shares a common body wiring harness with the gasser versions, it could be that the wiring and connector for this sensor is still there, but simply has a blank plug installed in the connector, usually nothing other than the mating connector shell with some rubber plugs shoved into it.

If that's the case, it could be that during the heavy rain mentioned the blank plug leaked for whatever reason, allowing enough water inside the connector to short across the contacts on the harness, triggering this "legacy" code in the software and throwing the warning light.

This practice of simply blanking off unused connectors on a standard wiring harness, depending on what options the customer does and does not want, is common at Freightliner.

Tinman · **Joined:** Mon Apr 10, 2006 10:45 am **Posts:** 308

litton wrote:

Don't mean to get sidetracked, but what is the "key trick" that allows you to retrieve the code?

tks

Turn the key on and off three times quickly without starting. After the last cylce, the trouble codes will flash up in the odometer window. This won't work on the '06s, at least not ours. Thanks D/C

. I have to get a OBD to ready the codes now.

BiodieselJeep.com · **Posted:** Tue Sep 19, 2006 2:37 pm

Thanks, retmil, that is an explaination that will let me sleep at night. Random wires shorting is a bit of a nightmare, but this makes sense. If I was a-retentive (which I am about cars) I would got looking for this relic sensor hole. But not this time.

Meanwhile, I have a increasing hard-start issue starting to annoy the primary driver (my wife), so I can go and obsess on that for a while (on top of tranny worries). I wonder what I used to do with my time before I had these diesels?

retmil46 · **Posted:** Wed Sep 20, 2006 11:32 am

BiodieselJeep.com wrote:

Thanks, retmil, that is an explaination that will let me sleep at night. Random wires shorting is a bit of a nightmare, but this makes sense. If I was a-retentive (which I am about cars) I would got looking for this relic sensor hole. But not this time.

Meanwhile, I have a increasing hard-start issue starting to annoy the primary driver (my wife), so I can go and obsess on that for a while (on top of tranny worries). I wonder what I used to do with my time before I had these diesels?

What I described is just a SWAG on my part, don't leave it at that. I would definitely get this checked out next time you're at the dealership. It could be something else altogether that is being affected by moisture/heavy rain, with the fuel cap code just a byproduct of what's going on. If it is an electrical glitch, it could happen again next time it rains, and next time there could be more serious results.

Coul be the hard starting and the electrical glitch are related problems.

Bottom line is, if you're having electrical/electronic problems from just driving in the rain, SOMETHING IS WRONG, and it needs to be fixed. I'm not trying to be an alarmist, but this does need to be looked at.

BiodieselJeep.com · **Posted:** Sun Sep 24, 2006 2:17 pm

So the CEL has been off last couple of days.

Sort of happened again today, though, no rain and no CEL. Thunderbolt (Electronic Throttle Control) came on flashing while we were out driving the baby to sleep for nap time (diesels are superior in this area, also). No rain, but rain in recent days. Stopped car, turned off and restarted, no CEL this time. Didn't bother to pull codes with no CEL...will do it later.

Gonna go to dealer probably soon anyways with the ball-joint recall in my future.

On a bright note, the baby is sleeping. Works every time.

Eh? P0624 Fuel Cap Lamp Control Circuit

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