I've tried everything on my 2000 Saturn SL2 to get rid of the P0340 code but nothing has fixed it. I've replaced spark plugs, plug wires, ignition coils, the ICM, and the fuel injectors but it still misfires on cylinder 1 and 4. I also cleaned the bolts that ground it but that didn't fix it either. Can anyone help me fix this?

 

Maybe an intake manifold gasket failure? IDK, just guessing. Derf is the resident S series guru. I'm sure he'll be checking in sometime today. Be patient.

 

Any other codes? Is the car actually misfiring or running rough?

Perform in the following order. Continue until the code goes away.
0) clear code
1) Run the stock ngk plugs NEW.
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Report back.

 

Does your car run rough and have more or less constant high idle?

I had a very similar issue and code on my 2000 SL at least 10 years ago. IIRC, it was a P0340 and it was accompanied by rough high idle and misfire. It turned out to be the infamous intake manifold gasket leak that plagued many of these cars due to a manufacturing defect on the assembly line (caused by a robot slightly crimping the gasket during installation to the engine block). Replacing the gasket fixed it and I have had no issues from it since. My car has the SOHC and yours (SL2) appears to have the DOHC engine, so not sure if that makes a difference as far as intake manifold gasket failure goes. One thing you might try is to squirt carb cleaner around the intake manifold gasket while it's idling and see if there's any drop in rpm. If so, that may be the culprit.

 

I would do a running compression test. Here's the TROUBLE tree. Glean what you can from it but be careful as it may have you replace a perfectly good PCM or similar.


Operation CHARM: Car repair manuals for everyone.
Home >> Saturn >> 2000 >> SL2 L4-1.9L DOHC VIN 7 >> Repair and Diagnosis >> A L L Diagnostic Trouble Codes ( DTC ) >> Testing and Inspection >> P Code Charts >> P0340

P0340

DTC P0340






The electronic ignition (EI) module supplies a ground to the cylinder #4 signal wire whenever it determines cylinder #4 has just fired on its compression stroke. The EI module uses capacitive pickup plates located under the 1/4 coil pack to determine the polarity sequence and voltage amplitude of the cylinder 1/4 secondary ignition. The powertrain control module (PCM) supplies 5 volts on the signal line and expects to see the cylinder #4 signal wire go low after every 14 crankshaft pulses (2 revolutions). This is used to determine the position of the camshaft, except under decel. The PCM only uses the transition from 5-0 volts as a valid TDC compression #4 cylinder signal. DTC P0340 sets when the PCM detects missing cam pulses (not seeing one cam pulse every two crankshaft revolutions).

DTC Parameters

DTC P0340 will set if the PCM cam pulse has not been properly detected (cylinder #4 signal line not pulled to ground) for 136 engine revolutions when manifold absolute pressure (MAP) is greater than 30 kPa.

If the PCM detects 20 correct cam pulses in a row, DTC P0340 will pass for the rest of the ignition cycle.

DTC P0340 diagnostic runs continuously until 20 correct cam pulses have been received when the vehicle is not in a decel.

DTC P0340 is a type B DTC.

Diagnostic Aids

Use a scan tool to monitor CMP RESYNC COUNTER while running engine. The counter should count to 14, which indicates the number of notches passed on the crankshaft in 2 revolutions, then reset to zero when a cam pulse is received.

High resistance in the #1 secondary ignition system or low resistance in the #4 secondary ignition system can set this DTC. Check for corroded or loose #1 or #4 secondary ignition components. Use a scan tool to monitor MISFIRE CURRENT CYL #1 and #4 which may point out an intermittent misfire causing the DTC.

A missing cam pulse without a cylinder misfire may not affect engine operation.





pro multis · About Operation CHARM

 

There's no cam sensor but that is a decent explanation of how the cam signal equivalent in an s car engine is used.

 

In general this only applied to the third generation SOHC engines.

Not to say that it could not be an issue with the intake manifold at two cylinders, but it's not likely related to what you mentioned about the assembly line oops.
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I asked him if the car has any other codes, because if it's not also showing p0301 and p0304 I would question why not?

In my experience PO340 goes away when you fix all the other outstanding issues with the ignition system.

By far the most common trigger for this code on Saturn s series engines is using plugs other than the OEM stock ngk plug gapped at 0.040.

At least no one asked where the cam sensor was.