2004 V70 T Seems NGK IX Iridium Spark Plugs Caused/contribute to CEM Codes Limp Mode Topic is solved

dono · Post by **dono** » 19 Mar 2019, 10:40

Installed NGK IX Iridium Spark Plugs (p/n BKR6EIX) in my 2004 Volvo V70 2.5T AWD wagon (Engine B5254T2 R5 2.5L) with 233,600 miles(replacing Bosch plugs) Thursday afternoon. Within 3 miles of driving car threw P0600, P0863, P0P0571 & P0504, went into limp mode. I restarted the car and cleared the codes and it ran another 4 miles till I got it home. Next morning it prevented starting because of comm failure w/transmission - same codes plus U0073 (bus communication). Disconnected battery, checked CEM ECU and TCU connections, cleared codes again, reconnected battery and car ran 10 miles without codes. Next morning codes and limp mode returned multiple times.

I called my 2 Volvo specialists and they suspected CEM starting to fail and did not see any relation to new plugs. I decided to bring the car in on Monday but had the weekend to tinker - concerned this might be the end of the vehicle for me ($2k to replace CEM) I decided to remove the NGK plugs and re-install the old Bosch Platinum plugs out of desperation - the problems and codes disappeared. My car has run fine since I removed the NGK plugs and the codes have not returned after several days of driving. Voodoo? Is my car allergic? Do the plugs play a role in CEM communicating to ECU TCU? Ill pick up a new set of Bosch platinum plugs and go my merry way but does anyone have insight into this? Ill report back if the codes return.

Post by **abscate** » 19 Mar 2019, 12:17

That’s a damn interesting story. It’s not definitive the new plugs are root cause as you flex and stress connections when you change plugs, but it’s strongly indicative at least.

Following this one intently...

Post by **chrism** » 19 Mar 2019, 13:57

I never had good luck using "designer" plugs in a Volvo. Going all the way back to our 1972 144, the cars just don't like them. But of course the auto parts stores will always tell you the latest platinum-titanium-iridium-kryptonite-whatever exotic metal is the way to go. They make lots of money selling them and it's irritating.

I've had the best luck with plain old single electrode copper core plugs like the ones you put in your lawn mower. I personally use NGK BKR6ES (NGK 6364) in our P2 cars for about $2.00 each - even cheaper online, and I typically get about 90,000 miles out of them. I believe Bosch and others sell a comparable plug also but I don't know the part numbers off hand. Oh, and also, in the 14 years we've been driving P2's I've never had to replace a coil. I say that because I've read posts where they are afraid of frying coils with copper core plugs due to improper resistance - hog wash.

Your owners manual will suggest Champion RC8PYP 8 (or equivalent) which may be hard to find in the US. But look at an image of that plug online - nothing fancy there.

93SCMax · Post by **93SCMax** » 19 Mar 2019, 14:18

I can tell you which plugs don't cause "limp home mode", and that's the OEM Volvo plugs. I believe they are manufactured by Robert Bosch. I've used Volvo plugs for 18 years and never had a limp home mode until my MAF needed to be replaced. I have Japanese cars (Nissan and Lexus) that hate German plugs (Bosch), and have learned that you only put Japanese plugs in Japanese cars. Clearly, some cars are pretty sensitive to the plugs you install. It may cost a little more up front, but sticking with OEM plugs may keep you from visiting your Volvo specialists.

I've never replaced a coil either. Maybe you have a coil/spark plug combination issue.

Post by **cn90** » 19 Mar 2019, 18:17

I installed the BKR6EIX plugs in my 2005 XC90 2.5T with 100K miles.
That was 3 years ago, zero issues, fuel mileage is better with Iridium plugs.

IslandV70 · Post by **IslandV70** » 20 Mar 2019, 08:58

Different plugs = different RFI levels. That might do it.

Post by **June** » 20 Mar 2019, 10:02

Also none of my Volvo cars over the years has ever had a coil, O2 sensor, or MAF sensor go bad. Or anything but flawless operation with Volvo brand plugs/ air filters. My 2004 S80 T6 has been burning gas for over 15years and 178K miles now. My next service is at 180K and spark plugs will be changed for the third time.

My car gets lots of idle with ac on in hot weather so I am sure my engine has well over 200k worth of rpm. Figure all the hot hours of idle in school lines waiting for my children all those years and now all the hours waiting on my parents several days per week. If heat was the issue with coil failure it would have already happened to my car. The few dollars more I pay for Volvo plugs every 60K isn't worth worrying about imho. June

dono · Post by **dono** » 14 Apr 2019, 16:29

It was definitely the plugs for me - no trouble codes since I took the NGK's out. I have run the Bosch OEM plugs for over 1,000 miles without any of the crazy issues I had with the NGK plugs. Very strange but you wont see me ever putting non-OEM plugs in my vehicles ever again...

93SCMax · Post by **93SCMax** » 14 Apr 2019, 16:32

So glad you were able to resolve your issue.

EngineeringBloke · Post by **EngineeringBloke** » 14 Apr 2019, 17:47

I would love to see what happens if you reinstalled the NGKs again

But that is asking a bit for my curiosity.