: SES Misfiring DTC P0300 My hunch is.....

04-04-05, 05:11 PM
....is this caused by the 'coil pack' 'ignition module'? (please see attached picture)

98 Deville is misfiring again. First time it was a bad plug wire. replaced all plugs and wires and problem solved) few months later it happened again, dealer replaced one of the four 'ignition modules' (sorry dunno what its called) pictured below. You can see the 2nd from the left (controlling cylinders 3 and 8) is new while the rest are the originals that came with the car.

The symptoms I have now are very rough idle, SES on and flashing sometimes, hiccuppy accelaration leads me to believe its one of the other three unreplaced 'ignition modules'.

It started a month ago with very slight hiccups while idling (i saw the rpm jump around 600-750 sometimes). Then last week, the SES light came on and it feels like I am running on 6 cyclinders.

I guess it could be another bad plug wire or spark plug but they are all new Ac Delco's only 1 year old........can plugged injectors, fuel filter or fuel rail cause this as well?

Should I take it to the dealer and have them diagnose it or should I gamble and buy a new one of these 'ignition modules' and try replacing on my own?

Any way I can isolate the problem?

DTC codes showing are:

PCM P0300
PCM P0463
PCM P0603
IPC B1552
SDM B1327

Please advise.

Thank you always.

04-04-05, 07:29 PM
Make sure that the intake manifold bolts are tight. I had the 300 code on my 98' eldorado. I changed the plugs and wires and I noticed that my intake bolts were loose.

04-04-05, 11:04 PM
You can easily swap out the coils one for another to see if the misfire changes. I think it's only two little bolts holding each one in place. If two cylinders are missing, it's probably another bad coil. There are four of them and they replaced one of them for you. You can get the ignition coils from various parts stores. I hate to keep advertising for Rock Auto, but they do have a good price on the coils at about $40 each. www.rockauto.com There is an AC-Delco coil and an Standard Motor Products coil. They look the same, but the SMP one is a dollar more expensive for some reason. Anybody know about the two brands? Obviously the Delco is the one to get, but why is the SMP higher price? Anyway, they have the coils you can easily replace it yourself. If you look through the forum, I have another post with a code to get an additional 5% off a Rock Auto order. When you do, just be very careful to plug the wires back in the same position they were before.

I would try swapping the coils around first to see if it changes. If so, then you can be reasonably sure it's a coil problem, then it's just a matter of tracking which one it is and replacing it with a new coil.

Let us know...

04-04-05, 11:55 PM
Two excellent tools to have to help you troubleshoot a problem such as your's is an inductive timing light and a mechanics stethoscope. Both of which can be picked up at your local auto parts store or even Sears.

You'll be checking for fuel and "fire" to all your cylinders with these two basic tools. Since the ignition(the "fire") is the most common problem, I would start by checking that system first as follows....

- Start the vehicle
- Take the timing light and connect it up to the battery terminals.
- Zip/cable tie the trigger ON and lay the timing light down somewhere where you can see it easily but securely away from falling into moving parts.
- Take the inductive pickup and clamp it onto each spark plug wire and watch for the timing light to flash. Each wire should produce a flash. If one or more is not flashing, you now have an idea where/what to go after. Otherwise, check the fuel system next...

- Start the engine
- Touch the tip of the stethoscope to each of the fuel injectors. You will hear "clicking" noises as the injector opens to emit it's fuel spray. Listen for ones that do not sound as loud or the same as the others.

Hope this helps to get you started in the right direction.

04-05-05, 12:37 AM
Thanks guys!

Michael: As far as swapping ignition coils around....do I have to buy a new one first? (I mean, if I swapped one of the existing coil packs with one of the other ones on there, the engine would still misfire (now in two other cylinders) right? So, unless I had some way of detecting which cylinders aren't firing, this wouldn't work........ leads to next question: I don't own an inductive timing light nor scanner, are there any ways to figure out which cylinders arent firing? (like from DTC codes?)

BlueMoon: sounds like those tools are great to have, I bet I can use the mechanics stetho to help isolate another one of my problems....a noisy pulley. (I cant tell where the sound is coming from) Is it cheaper to buy a inductive timing light or just drop 30-60 bucks on a new coil pack and see what happens?

.....I love this forum!

04-05-05, 12:39 AM
looks like inductive timing lights at sears run from 35-70$.....

04-05-05, 01:14 AM
You can spit on the exhaust ports to see which ones don't sizzle to find the dead cylinders and it's free. If you want to be a little more sanitary you can use a spray bottle of water. If you are really anal you can go to a welding supply store and get temp sticks to find the colder exhaust ports.

04-05-05, 04:12 AM
If you don't want to deal with hot stuff, you can pull each spark plug wire one by one (with the engine running), putting each one back as you go, to see which one has the LEAST effect on how the engine is running.

04-05-05, 06:24 AM
dkoz: Thats agreat idea, thanks for the suggestion! I think I'll try the water drop method. The thing I'm concerned about is, if the cylinder is not totally dead *ie. intermitten misfires* the temperature differential may not be large enough to detect this way. Also checked into temp sticks, looks like theres a wide assortment of sticks that melt at various temps, so I gotta narrow down the range of temps/sticks to make it efficient.

krashed: Thats sounds like a good plan too. In fact I was gonna do that. A concern here is that when I tried using this method last time I had the problem, pulling any of the plug wires off caused a very large difference in the way the engine idled. I wasn;t able to isolate which one caused the 'least' effect because the engine sounded so rough if any one of them were pulled. (again its probably due to the fact that the problem is intermitten)

Thanks for the tips guys!

Keep em comin :-)

04-05-05, 11:10 AM
Let it run in the mode that makes it run the worst to accentuate the problem. Maybe wet the exhaust with the engine cold and then see which ports dry first when you start it. The slow ones are the culprits. I have been doing it this way for over fifty years.

04-05-05, 02:01 PM
P0300 - Engine Misfire Detected
P0463 - Fuel Level Sensor Circuit High Voltage
P0603 - Control Module Long Term Memory Reset
B1552 - Keep Alive Memory (KAM) Error
B1327 - Vehicle system voltage below 9.0 volts

I think your alternator may be going bad... I'm guessing that if you put the air conditioning on, the misfires will get worse?

04-05-05, 02:59 PM
dkozloski: thats a great idea to prewet and watch them dry! Got my flashlight charged up, I am on my way. Thanks.

Krashed989: Thank you for taking the time to list the codes, I figured there was an electrical issue too. I posted on the electrical section that the car loses electricity when parkd sometimes. Sometimes its fine even after parking it for a few days, but sometimes I park for an hour, come back and find the remote doesn't work (nor the interior lights or anything) until I turn the car on and let it idle for a second. The wierd thing is the trunk pulldown seems to work even when the rest of the car is electrically off. Another obesrvation I made, when its in the electrically dormant mode and I go to start the car, if I dont start up the car on the first few cranks of the key, the dash lights up like a xmas tree and blinks a few times. I have to wait a bit before restarting.
Will they be able to check to make sure ots the alternator and not the battery at autozone? (the battery is about 1 year old die hard sears, the alt has been in the car since I got it 35k miles ago so it would be consistent)

Thank you

04-05-05, 03:22 PM
It doesn't take much power to run the trunk pull down motor. the dash board lighting up is probably from the antitheft devise. The alternator may be having a hard time charging the battery because the alternator is going bad. You should have it tested.

04-05-05, 08:34 PM
OK, just went out and tried to check it out....

I couldn't even see the exhaust manifold (so packed tight in the engine bay), so I couldnt try the water drop method....however since the problem is so intermitten I have a feeling its not gonna be obviously colder.

The ServiceEngine light went out, I think its because it didnt register a serious enough misfire in the last few engine on/off cycles. (its that intermitten) But the rough idle persists, and it surges under acceleration.

I tried pulling the plug wire off each of the four front side plugs, and I think I noticed (maybe, very subtle) that the #8 cylinder produced the least difference when disconnected. I couldnt get to the rear 4 cylinders to check, but I did disconnect the #3 wire from the coil. The arc shocked me :-( but it felt like it produced very little difference once again......so it may be the coil controlling 3 and 8 again. (it was replaced by the dealer to the tune of $350 less than a year ago.......do these things fail so quickly?)

Alternator: The battery Volts used to read about 14.1 volts when the car was running (past observation) but its now showing about 13.2-13.6 volts.

Kinda at a loss as for my next move.....

04-05-05, 10:39 PM
I rented (for free) an autoxray from checker auto to diagnose a misfire. The scanner will report codes p301-308 which will tell you what cyliner(s) are at fault.

04-06-05, 02:17 AM
Did you try turning the AC on to see if it gets worse? If its the alternator it will usually have more trouble when its under load.

Those coils shouldn't die out that fast. Unless they did something wrong when they installed it. I still have my originals on my 94 eldo.

04-06-05, 02:29 AM
I did actually. Starting the AC and/or putting the car in gear actually made it worse, but not by alot.

Would a failing alternator result in misfires? (Batt Volt reads 11.8 when the car is off and around 13.5 when its running)


Tommorow I am going to goto Autozone to try and borrow a scan tool. No checker autos around here and the closest thing Kragen Auto says they dont lend tools.

04-06-05, 03:17 AM
Yes it can. If its going bad it will still give power, but that power will be limited. Putting it under load will take more of that power and put it past its limit causeing everything to have a limited supply of power. Battery volts don't really tell you much about the alternator, just that its giving out some power.

You want to put an electrical load on it, not a physical load. Putting it into gear puts a physical load on the engine. Physical load should not effect the alternator much, if at all.

04-06-05, 06:46 AM
Mine does the same. Stutters bad. Under half throttle it will backfire. Changed plugs and wires 20,000 miles ago and didn't use AC Delco wires. Does anyone think wires can cause this? A friend thinks it may be fuel related, but I think my coolant temp would rise if there a cylinder was running lean. Anyone ever have fuel or injector problems?

04-06-05, 11:51 AM
Wxman: Yes, I over the past month have been intermittantly having injectors stick closed on my 96 ETC(Same symptoms & codes as PGlide). Very strange. It would either happen right from startup and stay that way the entire time the car was running or it wouldn't happen at all. First it was only cylinder #6, then it strangely happened intermit. to 2 others. In each case, the injector resistances and PCM outputs were good and I found it to be the pintles sticking in the injector(Gotta love that $15 stethoscope). I was able to free them by either applying a momentary 9 volts with a transistor battery or by tapping lighty on the side of them with a socket wrench. Worked fine for awhile, then kept intermittantly coming back.

It was like after the engine was hot and shut down, the remaining fumes would gum up the injectors and glue them closed for the next startup when the engine was cold.

Ran some fuel injector cleaner thru a tankfull after freeing them and seemed to go away for awhile but started happening again.

I was running gas from the same station all the time(Citgo). Switched to Shell V power(because it supposedly has more detergent) and so far no problems. Only time will tell tho.

This will be a good test to see if gasoline additives really make that much of a difference or maybe in my case, the previous owner had someone put sugar or something in the gas tank thats still showing up.

Powerglide, try borrowing a timing light from a buddy if you don't wanna buy one, but for sure get the steth. You can't see the exhaust ports on these cars and pulling off live plug wires is painful and Very hazardous to your health.

04-06-05, 05:56 PM

My original hunch turned out to be right, bad IGNITION COIL (cylinders 2 & 5)

Went to AutoZone and had an alternator test done, it was fine.
Next I borrowed their Scanner (Actron AutoScanner CP9135), hooked it up and read the codes, it only spit out one P0300. Said it was a random/multiple cylinder misfire........USELESS! My dash gives me more info than this thing.

Next I asked the guy at AutoZone if he knew how to check ignition coils (he didnt have an induction timing light for rent). There in a diagnostic book behind the counter was the directions for checking the coils.

Simple matter of measuring the resistance across the secondary (the ones on top) terminals. Checked all four (right there on the car) and found the last one reading an open circuit. I removed it right there in the autozone parking lot and measured the resistance across the rear primary terminals, same open circuit reading.

They had a new coil in stock, since I was pretty sure now that this was the culprit, and they had been very helpful isolating the problem, and I had removed the coil anyways, I bought one from them for $28.99.

It's a Duralast part number C849. I wish I could have put a AC Delco coil in ( they are 30$ at gmpartsdirect.com) but I wouldn't have felt right leaving AutoZone to go buy the part elsewhere after all the help they gave me.

It took another 50 seconds to bolt the new coil in place and the problem was fixed!!

I love autozone, cadillacforums, and everyone who posted here to help me out!

Thank you very much.

PS Last time I had the Caddy Dealer replace the coil. They charged me over $350!!! This time it cost me just $28.99. Makes you think.

04-06-05, 06:19 PM

My original hunch turned out to be right, bad IGNITION COIL (cylinders 2 & 5)

They had a new coil in stock, since I was pretty sure now that this was the culprit, and they had been very helpful isolating the problem, and I had removed the coil anyways, I bought one from them for $28.99. ....

Well done and thanks for the feedback on your findings.

04-06-05, 08:00 PM
The Cadillacs will typically only display PO300. Other GM products will display a specfic code such as PO304.

The GM Tech 2 will also just show PO300. But....it also will display a misfire graph that makes it very easy to determine which cylinder is missing.

There is a difference in what different scan tools will show.

Logan Diagnostic

04-13-05, 10:57 PM
Just an off the wall possibility...Rick94STS and my brother both had trouble with the intake manifold harness. The insulation flakes off and the wires were touching which gives random, almost undiagnoseable problems. It would be wise to take the plastic cover (the plastic conduit that keeps the wires together) off that harness and check the condition of the wires. It might save a lot of time.

The connector is under the throttle body, just follow the harness down. That is the area that was worse.

Infamous Lac
04-25-06, 07:19 PM
How do you measure the resistance on the coil pack.I have a multimeter