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2004 Jeep Grand Cherokee P0440 Code: Causes, Symptoms & Solutions for Intermittent EVAP System Issues

Model: 2004 Jeep Grand Cherokee Fault Code: P0440 Posted: 2014-01-03 15:28

I recently purchased a 2004 Jeep Grand Cherokee in 2007 and have been experiencing an intermittent Check Engine Light issue linked to code P0440. The problem started shortly after ownership and has fluctuated based on fuel level — the light typically comes on when the gas tank is filled above half full, and sometimes goes away if the tank remains below half capacity. During these periods, I was able to pass a New York State inspection because the code would disappear. Recently, however, the P0440 code has become persistent and stays active regardless of fuel level. Even after resetting the system, it returns immediately. My vehicle inspection is now 3 days overdue, and I'm concerned about whether I can pass it without resolving this issue. What could be causing this erratic behavior? Is there a specific component failure or design flaw in older 2004 Jeep Grand Cherokee models that leads to such intermittent P0440 readings? How might the presence of a remote starter (the only modification) influence EVAP system performance?

Related fault codes
P0440
Comments (8)
Anonymous 2014-01-03 16:36

This is a 2004 model year Jeep Grand Cherokee — could you confirm which engine variant it has? P0440 is not listed in my WJ (Wrangler) code database, so I'm wondering if the engine type affects this behavior.

Anonymous 2014-01-03 17:10

The vehicle is equipped with a 4.0L V6 engine. I've confirmed the P0440 code multiple times — it consistently appears under similar conditions.

Anonymous 2014-01-03 17:22

I rechecked the diagnostic codes and found that my system initially reported P0442, which is related to an EVAP leak detected at a medium level (0.040). I've also seen P0456 in the past — both are associated with evaporative emissions system leaks. Just now, after re-scanning, I received a new code: P0122. This has only appeared once before, several months ago, and I'm now seeing it again — this is quite confusing.

Anonymous 2014-01-03 18:23

P0442 – EVAP LEAK MONITOR MEDIUM (0.040) LEAK DETECTED — commonly known as a loose gas cap issue. The evaporative emissions system is typically tested using a smoke machine to detect leaks. Common leak points include: the fuel cap (green or yellow), purge valve, hoses connected to the charcoal canister (left and right sides, behind wheel wells), and connections near the master cylinder. P0122 – TPS VOLTAGE LOW — this is now showing up as a current code. Is it related to transmission shifting issues?

Anonymous 2014-01-03 22:48

I just ran a diagnostic tonight and confirmed P0122. This code appeared once before, about a few months ago, but I haven’t seen it since — until last night. That led me to suspect it might have been a false positive initially. Since then, I’ve noticed that at speeds around 40 mph, the transmission struggles to shift into higher gears and shifts with noticeable roughness when transitioning from 3rd to 4th gear. Could this shifting issue be related to P0122?

Anonymous 2014-01-04 12:30

A TPS (Throttle Position Sensor) fault could potentially affect transmission shift behavior, but I’d like to clarify — is your vehicle stock? Any modifications such as remote start systems, alarms, or aftermarket parts? If you have a scan tool, does it display all codes including those above P0999 (manufacturer-specific codes)? Does it show freeze frame data and real-time parameters at the time of code set? This information is critical for diagnosing root causes.

Anonymous 2014-01-04 13:33

I use a handheld OBD2 scanner I bought on eBay years ago. It only displays diagnostic codes and allows clearing them — it does not show live data or freeze frame records. The manual indicates it can read manufacturer-specific codes above P0999, though I haven’t seen one yet. The vehicle has had a remote starter installed since shortly after purchase — this is the only modification. The P0122 code appeared once before and remained dormant until last night. After clearing it, I’ve gone through several start cycles today without the check engine light coming back on.

Anonymous 2014-01-04 13:51

OBD2 scanners have limited diagnostic capabilities — ideally, we’d need to examine the freeze frame data at the moment P0122 was triggered. Every time you erase a code, you lose valuable emission test history, including data used by inspection stations during emissions checks. Currently, the only active code is P0442 (EVAP system leak). If this issue remains intermittent, it's worth closely inspecting the purge and vent valves — they may be stuck or partially obstructed, leading to inconsistent readings.