When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Hello,
My 2017 SL450 base with 81kmiles started to act like a dead cylinder the other day and through a code for #5. I parked and bought Denso coil pack, Bosch iridium plugs gapped at .028, and air filters and did a tuneup. #5 coil pack was blown. I checked codes and now it has P030022 random misfire. I tried using my icarsoft scanner, but it won't clear it. I tried disconnecting the battery in the trunk for a half hour, but no luck. I tried to reset using the gas pedal method, no luck. I checked all vac lines ok. Does this code have to "learn" itself off after a bunch of driving cycles? I use 93 fuel and maintain everything meticulously. Should I just drive it a week?
. Many
Thanks!
Get rid of the iCarsoft scanner and get a LAUNCH X431 Creader Elite 2.0 (or 3.0) BENZ. (Version 3.0 is available through Amazon and is considered worth the price difference over Version 2.0, but they both run the same Benz software.) LAUNCH should be able to clear “permanent” codes. If it can’t, you will need to use XENTRY.
Is the DTC current or stored? Is the CEL on?
Mercedes uses two suppliers: Bosch and NGK. Make sure you got the right brand for your engine. Also, you should replace all plugs at the same time and make sure they are properly indexed (search YouTube for indexing Mercedes plugs). With the correct plug, torquing to 23Nm should index the plugs correctly.
Last edited by PotatoHeadII; Jun 20, 2026 at 06:42 PM.
Thanks for the reply. Yes, the CEL is on solid. The engine runs and idles good, acceleration is smooth. It used to have a nice exhaust 'burble' after deceleration in Sport mode, but that's gone now. I will definitely look into plug indexing.
Thank You 👍
Thank you PotatoHead!!
I indexed the Bosch #96347 plugs. They were all out by about 100°. The copper washers were all .060 thick and I had to file them all to about .045 to get them to index nearly perfect. Running smooth and I was able to reset the CEL. I will note that I had disconnected both batteries and drained the caps initially, but the CEL was still on when I started it. I cleared it with the scanner though.
. Thanks again!
Mercedes SLR McLaren 722 S Is Extremely Rare Example Modified by McLaren
Slideshow: A one-of-one U.S.-spec Mercedes-Benz SLR McLaren Roadster became even rarer after a factory-backed transformation at McLaren's headquarters.
