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2005 Jeep Liberty 3.7L Engine P0204 Code: Cylinder 4 Not Firing, No Ground Signal from PCM

Model: 2005 Jeep Liberty 3.7 Fault Code: P2177 Posted: 2015-12-17 23:44

I'm experiencing a P0204 diagnostic trouble code on my 2005 Jeep Liberty with the 3.7L engine. Cylinder #4 is not firing despite good compression, new spark plugs, and I've swapped both the injector and coil to another cylinder. The Noid light flashes normally on all other cylinders but does not flash on cylinder #4. I have battery voltage on one wire of the injector connector and confirmed continuity from the injector to the PCM. This suggests that the Powertrain Control Module (PCM) is not providing a pulsing ground signal to the #4 fuel injector — which should be visible via the Noid light. I've also noticed an unrelated issue: when the alternator wiring is connected and the serpentine belt is engaged, the engine will not rev above 2200 RPM. However, if either the alternator wiring is disconnected or the belt is off, the engine revs normally. Replacing the alternator with a known good unit does not resolve this issue. The battery remains fully charged. I cleared the codes and started the engine with the alternator connected and belt off — no new codes appeared. Disconnecting the #4 coil had no effect on engine performance. After reconnecting the coil, clearing codes again, and reapplying the serpentine belt, the P0204 code returns. My question: Could the PCM be intentionally shutting down cylinder #4's injector operation for a non-injector-related reason (such as misfire or load conditions), without triggering an injector-specific fault code? If so, how can I confirm this behavior and diagnose the root cause?

Related fault codes
P2177
Comments (2)
Anonymous 2015-12-18 08:30

If the PCM detects a misfire in cylinder #4, it may shut down that cylinder's fuel injection to protect the catalytic converter. However, such an action would typically result only in a general misfire code (like P0304), not a specific injector fault code like P0204. Do you have a test light and a digital multimeter available? Are there any other diagnostic codes present that might indicate underlying issues?

Anonymous 2015-12-18 11:45

I do have both a test light and a digital multimeter. To be absolutely clear — if the PCM shuts off fuel injection to cylinder #4 for any reason other than a faulty injector (e.g., due to misfire or sensor feedback), would it still not generate a P0204 code? Or is there another way this behavior could manifest?