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2004 Ram 2500 P0499 Fault Code: Diagnosing Purge Solenoid and LDP Issues

Model: 2004 Ram 2500 Fault Code: P0499 Posted: 2015-07-11 12:13

Hi everyone, I'm looking for help diagnosing a persistent P0499 error code on my 2004 Ram 2500. The engine light is on, and I've already replaced both the purge solenoid and the LDP (Large Diameter Pump). I want to confirm whether the issue lies with the wiring harnesses, the ECM, or if there's a deeper system fault. Here’s what I’ve done so far: - With the key ON, I measured voltage at the 2-pin purge solenoid connector: 12V on one wire and 11.7V on the other. This reading appears consistent with an unpowered state. - When I connected the black wire from the purge harness to the 3-pin LDP connector, I observed 12V on one wire and no voltage on the other two. I’ve also checked for evaporative system leaks and replaced all suspect hoses—no signs of leakage or physical damage. Unfortunately, I don’t have access to a scan tool that can activate the purge solenoid. Without activation, I’m unable to verify if the valve is functioning properly. My question: How should I proceed to test the wiring harnesses? Should I check for continuity or ground faults in the purge solenoid and LDP circuits? Is it possible that the ECM is stuck in a high-resistance state (e.g., failing to ground the purge solenoid)? Any guidance on next steps—such as using a scan tool, testing with known-good equipment, or replacing the ECM—would be greatly appreciated. Thanks in advance, Jim

Related fault codes
P0499
Comments (9)
Anonymous 2015-07-11 12:58

P0499 specifically indicates an issue with the evaporative emissions system purge valve circuit. Confirming this code is critical before proceeding with diagnostics.

Anonymous 2015-07-11 13:20

I don’t have a scan tool either, so I’m not sure what the expected voltage readings should be under normal conditions—anyone know if 12V and 11.7V on the purge solenoid is within acceptable range?

Anonymous 2015-07-11 14:37

Can you confirm that the code displayed in your vehicle is actually P0499, not a similar code like P0449? I’ve seen confusion between these codes before.

Anonymous 2015-07-11 14:59

Thanks for clarifying—yes, I verified it at an auto parts store with their diagnostic tool and the code is indeed P0499. The voltage reading of 12V on one wire and 11.7V on another across the purge solenoid coil appears normal when unpowered. I also tested continuity by pulling the PCM connector—no issues found there.

Anonymous 2015-07-11 15:40

According to official technical documentation, P0499 points to a fault in the purge valve circuit, which may involve wiring, a faulty solenoid, or an ECM issue that fails to properly ground the valve.

Anonymous 2015-07-11 15:43

Apologies—yes, I meant to say P0499, not P0449. The earlier confusion was due to mixing up codes. This is a purge solenoid issue, not a vent valve one.

Anonymous 2015-07-11 16:00

I initially thought 'vent valve' referred to the purge valve, but I may have been mistaken. My truck has an LVP (Large Vent Valve) located near the charcoal canister—does it have a separate vent valve on the fuel tank or elsewhere? It doesn’t appear there is one directly on the canister.

Anonymous 2015-07-11 16:27

I haven't worked with this component before, but based on standard setups, there may be a vent valve near the fuel tank. The voltage reading of approximately 12V to 11.7V across an unpowered solenoid coil is normal. A possible issue could be an open wire or connector in the purge circuit—without a scan tool, it's hard to confirm.

Anonymous 2015-07-11 18:03

I believe this points to the purge vent valve. My evaporative system diagram shows no dedicated vent valve on the canister. The voltage reading (12V and 11.7V) across the coil is normal when unpowered. I suspect the ECM may be stuck in a high-resistance state—normally it should ground the solenoid during purge cycles. My next step will be to take the truck to a shop with a scan tool that can activate the purge valve. If the valve doesn’t respond, then the ECM is likely faulty. Any additional insights would be helpful!