Gas cap warning light

John Warner · #1 03-30-2006, 10:43 AM

A Ford dealer service department found the reason my 2002 F-150 4X4 was getting a warning light for a loose gas cap and check engine light. As it turns out there, the reason for warning lights is an emissions canister over my gas tank that has a corroded electrical connector powering the canister's solenoid. The dealer says that it will take a couple of hundred dollars to fix it, after all parts are ordered and installed. They say it does not hinder normal performance except for the annoying lights. Has anyone ever bypassed this device with any success, or cleaned up the connector with any success?

bigdaddyII · #2 03-30-2006, 10:51 AM

My check engine light came on, pulled codes and turned out to be gas cap, replaced gas cap and never had light since. Havent heard of it being bypassed though. I wouldnt pay hundreds of dollars just to turn a light off.

Pre-Runner · #3 03-30-2006, 03:37 PM

low budget non ( dealer ) advice taking side of me says... disconnect battery for four hours...during this four hour period go purchase replacement gas cap... come back install gas cap...re-connect battery cable... if problem never re-presents itself never return that dealer for service.. JMO

projectSHO89 · #4 03-31-2006, 07:26 AM

Without the exact DTC codes, it's pretty pointless to guess WHY the CEL came on and what diagnostic procedure was followed.

A loose or leaking fuel cap can cause several DTCs, namely a P0442, P0455, or a P0456. All of these have mulitple causes, the cap is only one possibility.

Since my tech library only goes to 01, I do have a question. Do the 02's and up have a separate GAS CAP light in the dash? If so, can someone who has the later service docs look up the circuit and describe how it works? I'm curious.

Steve

GIJoeCam · #5 03-31-2006, 03:30 PM

IIRC, if the evap canister purge solenoid sticks open, it allows air to be drawn through the fuel tank and into the engine the same way as if you left the fuel cap off. It simply draws it through the vents instead of through the cap, that's all.

I wouldn't say for sure that the evap cannister is your problem, but caouldn't say for sure it's not either. I'd be asking what diagnostic procedure led them to that conclusion. The problem they're suggesting fits the symptoms, but there are a couple other problems that can cause the same symptom.

-Joe

Quintin · #6 03-31-2006, 07:37 PM

Quote:

Originally Posted by projectSHO89

Since my tech library only goes to 01, I do have a question. Do the 02's and up have a separate GAS CAP light in the dash? If so, can someone who has the later service docs look up the circuit and describe how it works? I'm curious.

Steve, I'm looking at the '02 WSM, and it appears they do have a seperate gas cap light. According to the description in the book, the PCM will try to pull a target vacuum in the fuel tank after a refill. If it can't reach this vacuum, it'll set P0457 and provide ground to the instrument cluster, turning the "Check fuel cap" light on. FWIW, the Escape, Windstar, Mustang, Continental, Town Car, Thunderbird and LS don't have a dedicated wire going from the PCM to the instrument cluster for this, it's done through the BUS -/+ circuits via the SCP network.

GIJoeCam · #7 04-01-2006, 04:41 PM

Quote:

Originally Posted by Quintin

Steve, I'm looking at the '02 WSM, and it appears they do have a seperate gas cap light. According to the description in the book, the PCM will try to pull a target vacuum in the fuel tank after a refill. If it can't reach this vacuum, it'll set P0457 and provide ground to the instrument cluster, turning the "Check fuel cap" light on. FWIW, the Escape, Windstar, Mustang, Continental, Town Car, Thunderbird and LS don't have a dedicated wire going from the PCM to the instrument cluster for this, it's done through the BUS -/+ circuits via the SCP network.

True, but the system also needs to have the cannister purge valve closed when it's performing that test. That's why a purge valve stuck in the open position can trigger that light. As far as the system knows, the most common source for that type of gross evap system leak would be a fuel cap someone forgot to replace after refueling. It still could be either the bad valve//solenoid or a bad fuel cap. I'd want the tech to explain to me why it's NOT the cap and why it IS the valve before I OK the replacement.

-Joe