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2004 Chevy Classic with P0340 Code: No Symptoms, Recurring After Ignition Part Replacement

Model: 2004 Chevy Classic Fault Code: P0340 Posted: 2017-06-20 22:12

My wife's 2004 Chevrolet Classic is displaying a persistent P0340 diagnostic trouble code, which indicates a camshaft position (CMP) sensor issue. Despite no noticeable symptoms—such as misfiring, stalling, or poor performance—the code returns after clearing the system. This raises concerns about whether the fault lies in wiring, the powertrain control module (PCM), or another component. The vehicle is based on the 2004–2005 rental version of the Chevrolet Malibu, equipped with a base 2.2L L61 Ecotec engine. Recently, the car began sputtering and losing power before I replaced the spark plugs and ignition coil. After this repair, the vehicle ran smoothly for several days, but the P0340 code reappeared the next day—though no performance issues have been reported since. I'm seeking insight into whether the P0340 code might be related to a 'synthesized' signal from the ignition module (ICM), particularly given that the engine uses an ion-sensing camshaft position system. This technology relies on detecting current flow during spark plug firing to determine cylinder compression state, which helps the PCM identify when a cylinder is in compression versus exhaust. Given that only the plugs and coil were changed before the code appeared, I'm wondering if this could be a symptom of an ignition module failure or compatibility issues with aftermarket parts. Any guidance on diagnosing or troubleshooting this specific P0340 scenario would be greatly appreciated.

Related fault codes

P0340

Comments (5)

Anonymous 2017-06-21 10:30

Could you clarify your location and the exact engine type? The Chevrolet Classic is not a standard North American model—though it was produced briefly as a rental variant of the Malibu. It's equipped with the base I2.2 L61 Ecotec engine, which uses an ion-sensing camshaft position system.

Anonymous 2017-06-22 23:27

The Chevrolet Classic is indeed an American model, produced in 2004–2005 as a stripped-down rental version of the Malibu. It features the base 2.2L L61 Ecotec engine, which uses ion-sensing technology for camshaft position detection.

Anonymous 2017-06-23 07:12

This is an interesting case—similar to what's sometimes called the 'Iraqi Taxi' configuration due to its rare and simplified design. I’ll need to verify the specific engine model and find a comparable vehicle for reference. However, it’s worth noting that in some L61 Ecotec engines, the camshaft position signal may be synthesized by the ignition module (ICM) based on spark plug current flow during firing cycles. Have there been any recent maintenance activities—such as spark plug or coil replacement? This could impact the ion sensing accuracy.

Anonymous 2017-07-12 09:47

The vehicle is actually quite basic and not widely known, but it does have the L61 Ecotec 2.2L engine. A few weeks ago, it started sputtering and losing power—after which I replaced just the spark plugs and ignition coil that same evening. The issue resolved immediately. However, a new P0340 code appeared the next day when my wife went to the store. Since then, no performance issues have occurred, though the code remains present. I’m unsure how this relates to the ion-sensing system. Could you explain more about how the ignition module contributes to camshaft position signal synthesis?

Anonymous 2017-07-12 12:38

A key observation: there was no P0340 code before the spark plugs and coil were replaced. This suggests a possible link between the ignition system components and the synthesized CMP signal. The ion-sensing process relies on detecting current flow during spark plug firing to determine whether a cylinder is in compression or exhaust phase. When a cylinder fires in compression, it creates a distinct current signature that allows the PCM to identify when #1 cylinder is in compression (as opposed to exhaust). This information is used to synthesize the camshaft position signal. If aftermarket parts—such as plugs or coils—are not fully compatible with this system, they may disrupt the ion sensing process. While the ignition module (ICM) is a potential suspect, the fact that only the plugs and coil were changed points toward this being the root cause. I would recommend checking for compatibility of the parts used (e.g., AC Delco), ensuring proper boot installation, and applying dielectric grease. For reference: in paired cylinders (1@4), one fires at TDC while the other is in exhaust—this creates a measurable difference in current flow that the PCM uses to determine timing.