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2007 Chevrolet Silverado 5.3L Fuel Evaporative System Fault: How to Fix EVAP Code and Pass Oregon Emissions

Model: 2007 Silverado 5.3 Fault Code: P2177 Posted: 2015-01-02 10:29

I'm troubleshooting a persistent EVAP system fault on my 2007 Chevrolet Silverado 5.3L with an active OBD2 code related to the fuel intake and evaporative emissions system. When I tested the voltage at the vent solenoid connector, I observed a difference: 12V when the key is off (KOEO), dropping to approximately 0.04V or 0.07V when the key is turned on. This behavior suggests an issue with the solenoid circuit. According to forum guidance, when the ignition is ON and engine OFF (KOEO), both wires at the vent solenoid connector should ideally have 12V. The white wire should remain at 12V until the PCM commands a ground — which causes it to drop to near zero volts, allowing the solenoid to close. However, in my case, only one wire (pink) consistently reads 12V when the key is off; the white wire shows only 0.04–0.07V when the key is on. I have confirmed that the solenoid itself functions properly when tested independently with a battery. The issue appears to be in the wiring or connector at the vent solenoid, possibly due to poor contact, a broken wire, or an open circuit. I am now trying to locate pin 61 (X1) on the PCM connector as suggested earlier — but I don't have access to diagrams or photos of this connection. My main concern is that I may be facing a faulty PCM, especially since I cannot pass emissions in Oregon with an active EVAP code and my plates are expired. The truck is my daily driver, so resolving this quickly is critical. Can anyone provide clear wiring diagrams or photos showing where to test the voltage at the PCM side of the white wire? Is it possible that the PCM isn't sending 12V to the white wire — or is there a more likely issue with the connector? I’ve also learned from another user’s experience: removing the truck bed and inspecting the fuel tank revealed a damaged strainer causing refueling issues for years. That fix helped, but I still need to resolve the EVAP code (code 449) permanently to pass emissions. Any help identifying where to test voltage at the PCM or confirming whether a new PCM is required would be greatly appreciated.

Related fault codes

P2177

Comments (12)

Anonymous 2015-01-02 11:38

When you back-probe the vent solenoid connector, ensure both wires have 12V when the key is ON and engine OFF (KOEO). Test the solenoid's resistance with an ohmmeter — it should show a low value (typically under 5 ohms) indicating good continuity. If the reading shows open circuit or infinite resistance, the solenoid itself may be faulty. Disconnect the connector and perform your test light check as instructed. I’ve sent you an email through this forum — feel free to reach out for PCM connector diagrams. Also verify that the solenoid connector has no contact issues.

Anonymous 2015-01-06 17:20

On a separate but equally important issue, I removed my truck bed and accessed the fuel tank. After taking off the filler neck, I discovered the strainer was knocked sideways — it had been blocking fuel flow for years. This explains my long-standing refueling problems. Thank goodness this is now fixed! The only remaining hurdle is clearing code 449 permanently.

Anonymous 2015-01-20 12:20

Hi AutoJoe! I’ve been looking for that PCM connector diagram you mentioned earlier. Also, if I need to replace a component, what should I be buying? I tested the vent solenoid connector and found 12V on one wire (pink) regardless of key position — but the white wire consistently read near 0VDC. Does this mean I need a new PCM? Please help! I just got a ticket for driving with expired tags because I can’t pass emissions with an EVAP code. This is my daily driver, and I need it working again. Any advice would be very much appreciated! Doug

Anonymous 2015-01-20 13:40

AutoJoe — please confirm: when the vent solenoid connector is plugged in, you should test for 12V on both wires. If only one wire has voltage, that points to a problem with the valve or its electrical connection. In earlier posts, we described the wire colors — pink and white. When unplugged, only one wire should have 12V. When plugged in, both should ideally show 12V.

Anonymous 2015-01-20 14:24

Hello Kev2. I tested the solenoid connector with it plugged in — and again with it unplugged. In both cases, one wire reads 12V and the other is near 0VDC. But I know the new solenoid works because I tested it directly on a battery. So when plugged in, do both wires have 12V? No — only the pink wire has 12V; the white wire shows 0.04V or 0.07V (key-on).

Anonymous 2015-01-20 15:00

I’ll try to explain clearly: check the electrical connector carefully. When connected, current flows from the power source (pink wire) through the solenoid — so both wires should have 12V when plugged in. If not, inspect the connector for damage or poor contact. Available at auto parts stores if needed. If there’s no voltage on the white wire when the connector is plugged in, the EVAP code will set because the PCM won’t detect a proper circuit — it expects to see 12V on that wire.

Anonymous 2015-01-20 15:36

Thanks for clarifying. When I tested with the solenoid connector plugged in, I saw 12V on the pink wire and only 0.07V on the white wire — not 12V. This was done while the key was turned to ON. If I understand correctly, when the ignition is off (KOEO), both wires should have 12V. When the key is turned on, the white wire should drop to near zero volts — creating a voltage differential that closes the solenoid. Is this correct? If so, why isn’t the white wire showing 12V at all?

Anonymous 2015-01-20 16:29

With key ON and engine OFF (KOEO), both wires should have 12V. The white wire runs to the PCM — when commanded, the PCM supplies a ground. This causes the voltage on the white wire to drop as the solenoid operates. The PCM monitors this circuit: it expects to see 12V on the white wire. Remember — the white wire is NOT grounded. If there’s no voltage change when the PCM commands a ground, the code will set. It appears the wiring at the vent connector may be open — no power reaching the valve.

Anonymous 2015-01-21 12:29

So is this a PCM issue or something else? I do see a small voltage (0.04–0.07V) on the white wire when turning the key on — and it's consistent at the back of the connector. Based on your explanation, is the white wire receiving power from the PCM? Can you please post a photo showing where to place a multimeter to verify if the PCM is actually sending 12V to the white wire? Doug

Anonymous 2015-01-21 12:59

I believe the issue lies in the vent solenoid connector — the white wire isn’t making proper contact with the valve. This could be a broken wire or internal connection failure. There is 12V at the pink wire from the fuse box. BUT — there is NO 12V on the white wire when the connector is plugged in. The white wire is NOT grounded. The PCM does NOT send 12V to the white wire. Instead, it sends a ground signal. The system requires voltage on the white wire to complete the circuit — and if that voltage isn’t present, the code will set.

Anonymous 2015-01-22 08:35

Doug: You mentioned testing with key off and engine off. I think there may be some confusion here. When Kev talks about KOEO (Key On, Engine Off), that’s what we mean — not when the engine is running.

Anonymous 2015-03-04 12:16

Well, my emissions issues were actually resolved by reseating the vent solenoid connector. I had inspected it two weeks ago and found loose connections — after re-plugging it in and clearing the codes, my OBD2 reader showed no active faults. I took the truck to DEQ and passed emissions with no codes. My fix-it ticket dropped from $110 to just $35! Thanks to everyone for your help — I’m now fully compliant again.