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2002 Jeep Grand Cherokee 4.7L V8 P0201 Code: Rough Running Diagnosis and Fix

Model: 2002 Jeep Grand Cherokee Fault Code: P0201 Posted: 2016-07-31 12:54

I own a 2002 Jeep Grand Cherokee with a 4.7L V8 engine, and I'm currently experiencing a rough idle and a persistent OBD2 code P0201. After running through standard diagnostic steps—such as measuring injector resistance (Injector #1 reads 13.9 ohms vs. Injector #2 at 14.1 ohms)—I swapped the injectors to test for consistency. The same P0201 code appeared after the swap. While testing with a test light, I observed voltage on the positive side and pulsing on the signal wire when the engine was running—indicating that the injector circuit is active. However, this does not confirm proper operation. My initial conclusion was that the Powertrain Control Module (PCM) might be faulty. But after further investigation, I discovered a more fundamental issue. I performed a compression test and found zero compression in cylinder #1. This led me to suspect a mechanical failure—specifically, a burnt or detached intake valve seat. After removing the cylinder head, I confirmed that the intake valve seat had completely separated from the head, preventing proper valve closure and resulting in no compression. This mechanical issue is likely the root cause of both P0201 and other related misfire codes (P0300, P0301, P0302, etc.). Once I replaced the cylinder head and reinstalled it properly, all trouble codes cleared. This confirms that the P0201 code was not due to a faulty injector or PCM but rather a mechanical failure affecting engine performance. Key takeaway: Always investigate mechanical issues like valve train problems before concluding that an electronic component (like an injector or PCM) is at fault—especially when multiple misfire codes are present.

Related fault codes
P0201
Comments (7)
Anonymous 2016-07-31 12:56

Clear the diagnostic trouble code to ensure it's not intermittent. The signal wire should pulse when the engine is running—the pulsing indicates that the PCM grounds the injector circuit during fuel injection cycles. Check for damaged wiring or connectors in the injector harness, especially where it may be rubbed against the engine or body. Also review the freeze frame data (stored diagnostic information) to see if there are any patterns before making a diagnosis.

Anonymous 2016-07-31 14:11

I'm not familiar with 'freeze frame'—thank you for clarifying! I did follow your advice and swapped Injector #3, not #2. After that, I ran a compression test and found zero compression in cylinder #1. Could this explain the P0201 code? My next step was to remove the valve cover, inspect the camshaft, and perform a leakdown test to assess for internal leaks or mechanical failure.

Anonymous 2016-07-31 16:17

Are there any other codes present—such as P030x? If you're relying on a scanner, avoid using 'key dance' tricks. The PCM should detect a consistent 12V signal from the injector and see it drop when grounded during injection cycles. A lack of expected voltage suggests an issue with the injector or wiring. Given your zero compression in cylinder #1, this is likely the primary concern.

Anonymous 2016-07-31 17:31

Yes, I initially had several codes: P0300, P0201, P0301, P0141, P0302, P0304, P0155, and P0161. I focused on P0201 because misfiring injectors can trigger other codes. After removing the valve cover, I applied air pressure to cylinder #1—air flowed through the intake at about 40 psi, indicating a leak. For cylinder #3, no airflow was detected. This suggests a burnt or stuck intake valve is likely the issue.

Anonymous 2016-08-01 08:39

You should prioritize resolving the compression issue first. When the cylinder head is removed, inspect all injector harness connections and wiring for damage. Also verify that the intake valve was not opening during the compression test—ensure you were testing on a compression stroke. O2 sensor codes like P0141, P0155, and P0161 are typically related to heater circuits; check fuses, relays, and wiring before replacing sensors. See: https://www.obd-codes.com/p0141, https://www.obd-codes.com/p0155, https://www.obd-codes.com/p0161.

Anonymous 2016-08-01 14:20

With zero compression in cylinder #1, I removed the cylinder head and found that the intake valve seat had completely detached from the head. This explains why the valve never closes—resulting in no compression. After replacing the cylinder head assembly, all codes cleared. I'll update once I've completed the rebuild and verified engine performance.

Anonymous 2016-08-15 11:09

** UPDATE ** After replacing the cylinder head, all diagnostic trouble codes have disappeared. The issue was entirely mechanical—no injector or PCM failure. This confirms that P0201 was triggered by a failed intake valve seat and loss of compression. A mechanical repair resolved the problem completely. I would have preferred a faulty injector, but in this case, it was clearly a structural engine component failure.