Code PO340 Again
Super Moderator
Joined: Apr 2015
Posts: 3,229
From: Willamette Valley, Oregon
Probably won’t misfire until the compression is under 100. Just went through a misfire code on the L61 in the Alero. Compression close to 175, plugs looked good so I reversed 1-4 to see if the misfire followed the plug and replaced the coil pack. Car runs good now but time will tell.
Thread Starter
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Junior Member
Joined: Mar 2025
Posts: 4
From: Greenwood IN
PO340 Fixed
Solved the problem. Bought a ACDelco Ignition Module from Rockauto. I am returning the cheap one I bought from them. So do not buy a cheap part for this Ignition module.. Lesson learned. Next is valve cover gasket and serpentine belt with cracks in it. Thanks to everybody here for the help. Russ.
Junior Member
Joined: Aug 2024
Posts: 8
P0340 code: New ign module did not fix it.
Hi guys -
My son's 2002 coupe would not start, so I replaced the plugs, wires, ign coils and module. however, the P0340 code still comes up. After replacing the module, I drove it for 6 miles with no CHECK ENGINE light. Then, I shut it off, started it up right away and I noticed that there was a slight engine miss/hesitation within 5 seconds of starting the car. At that point, the CHECK ENGINE light came on. What do you think? Any help from you is much appreciated!
Steve M.
PS - It seems to me that there is a good ground connection from the ignition coil/module bolts and towers. I sanded/scotch-brighted all relevant parts.
My son's 2002 coupe would not start, so I replaced the plugs, wires, ign coils and module. however, the P0340 code still comes up. After replacing the module, I drove it for 6 miles with no CHECK ENGINE light. Then, I shut it off, started it up right away and I noticed that there was a slight engine miss/hesitation within 5 seconds of starting the car. At that point, the CHECK ENGINE light came on. What do you think? Any help from you is much appreciated!
Steve M.
PS - It seems to me that there is a good ground connection from the ignition coil/module bolts and towers. I sanded/scotch-brighted all relevant parts.
Super Moderator
Joined: Jul 2005
Posts: 12,315
From: Slightly off center
Did you put it in OEM plugs?
Not implying that alone would keep the car from starting, but it may lead to a p0340 if they are not OEM
Did you buy cheapy ICM and cheapy coils? Not saying you did, simply asking you the question, as some of the cheaper parts has demonstrated above simply don't play well in the s car ignition system. Also, please realize that changing more than one thing at a time makes it extremely difficult to pinpoint what part of the system is actually failing to behave as expected.
I've had people I've met in parking lots come to my house to sort out p0340 and p 0341.
I give them an old set of OEM spark plugs that is still good. If that doesn't work, I give them an old set of AC Delco plug wires. Between the two, I've remedied every single situation. Obviously that's not going to work if it's the ICM and no I don't give those away nor have any extras. Reread above if you have purchased a cheap ICM.
Not implying that alone would keep the car from starting, but it may lead to a p0340 if they are not OEM
Did you buy cheapy ICM and cheapy coils? Not saying you did, simply asking you the question, as some of the cheaper parts has demonstrated above simply don't play well in the s car ignition system. Also, please realize that changing more than one thing at a time makes it extremely difficult to pinpoint what part of the system is actually failing to behave as expected.
I've had people I've met in parking lots come to my house to sort out p0340 and p 0341.
I give them an old set of OEM spark plugs that is still good. If that doesn't work, I give them an old set of AC Delco plug wires. Between the two, I've remedied every single situation. Obviously that's not going to work if it's the ICM and no I don't give those away nor have any extras. Reread above if you have purchased a cheap ICM.
Last edited by derf; Jun 6, 2025 at 03:26 PM.
Super Moderator
Joined: Jul 2005
Posts: 12,315
From: Slightly off center
Pardon me, I misread your post. You got the flashing check engine light which is indicative of an active misfire. So you should have a p0300 to p0304 stored code. We have to determine what cylinder it is if it is in fact indicating a single cylinder. Read the code and we'll take it from there. In all likelihood, will probably need to do a compression test to see if that cylinder has low compression or anything else going on that could lead to a misfire like an oil fouled plug, etc
Junior Member
Joined: Aug 2024
Posts: 8
Code P0340: new ICM didn't fix it.
Hi Derf-
Thanks for the quick response.
I bought plugs, wires and ICM from RockAuto and did not buy OEM. Instead, they are mid-price ranged.
I appreciate your advice and have a follow up question:
Could my observation regarding the CHECK ENGINE light appearance, upon the second start-up be a clue?
I think that it's strange how the engine ran fine for 10 minutes, then I shut it off, and restarted and then I got the CHECK ENGINE light.
If helpful, here is my code display (from my Autel OBD): "Camshaft position sensor A circuit bank 1 or single sensor".
I'll wait to hear back from you before proceeding further. I look forward to your reply.
Thanks again!
Thanks for the quick response.
I bought plugs, wires and ICM from RockAuto and did not buy OEM. Instead, they are mid-price ranged.
I appreciate your advice and have a follow up question:
Could my observation regarding the CHECK ENGINE light appearance, upon the second start-up be a clue?
I think that it's strange how the engine ran fine for 10 minutes, then I shut it off, and restarted and then I got the CHECK ENGINE light.
If helpful, here is my code display (from my Autel OBD): "Camshaft position sensor A circuit bank 1 or single sensor".
I'll wait to hear back from you before proceeding further. I look forward to your reply.
Thanks again!
Super Moderator
Joined: Jul 2005
Posts: 12,315
From: Slightly off center
Do you still get the check engine light flashing when you drive the car?
Have you read the codes since getting the flashing check engine light? I know you put down what you observed the last time you read codes, but it is not clear when that occurred. Was that before or after the flashing check engine light?
Please put a set of OEM plugs in there, clear the codes and drive a longer distance without turning off the engine. Misfires or events detected as misfires by the ignition system occur for many reasons. If OEM plugs do not cure this all, then we will go to the troubleshooting tree.
Have you read the codes since getting the flashing check engine light? I know you put down what you observed the last time you read codes, but it is not clear when that occurred. Was that before or after the flashing check engine light?
Please put a set of OEM plugs in there, clear the codes and drive a longer distance without turning off the engine. Misfires or events detected as misfires by the ignition system occur for many reasons. If OEM plugs do not cure this all, then we will go to the troubleshooting tree.
Senior Member
Joined: Jan 2024
Posts: 623
From: Davison, MI
Probably won’t misfire until the compression is under 100. Just went through a misfire code on the L61 in the Alero. Compression close to 175, plugs looked good so I reversed 1-4 to see if the misfire followed the plug and replaced the coil pack. Car runs good now but time will tell.