CarTalk.com Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

Issues with GM cars and Bosch electronic replacement parts

I am curious as to whether others on the forum have had compatibility issues with GM vehicles and Bosch replacement electronic parts. 5 years ago, I owned a 1998 Malibu LS with a 3.1L engine. When it came time to replace the original spark plugs at 240k kms, I decided to use Bosch Platinum plugs and a new set of plug wires (not sure of brand). Shortly after replacing the plugs, the car began misfiring randomly on all 6 cylinders. I own an OBD-II code scanner, which I was able to use to verify which plug/coil was misfiring, and began replacing what I thought were faulty coil packs with new coils, which made no difference. After a few weeks of coil swapping and numerous other attempts to stop the misfiring, it occurred to me that this all began with the servicing of the plugs. So I went out and bought 6 new AC Delco OEM replacement plugs, installed them, and never had another issue until I sold the car a year later.

Skip to present day. I now own a 2001 Monte Carlo LS, 3.4L engine, with 285k kms. I’ve owned the car 4 years with very little issues, aside from regular maintenance items. Just recently, I had to replace the upstream O2 sensor, due to the heating element not working anymore. I picked up a replacement part, which was a Bosch part, and while replacing the original sensor, checked the wiring harness for chafes and breaks, which I could not find. I did not, however test the voltage with a voltmeter because of the good condition of the wires and connector. The new sensor worked ok for about a month, until this week when I noticed my MPG decreasing and eventually, the CEL illuminating. When I plugged in my scanner, it brought up a P0134, “O2 sensor circuit, no activity detected, bank 1 sensor 1”, which tells me the replacement Bosch sensor I installed is either a) defective, or b) once again, refusing to cooperate in my non-German, American GM built car. I have already arranged to bring this sensor back under warranty and replace it with another brand, and pay the difference in price. I will also test the connector for proper voltage readings, which I am not expecting to find issues with.

Is it just me, or have others encountered these types of problems with Bosch products and their GM, or other NA built cars? I have used Bosch parts on other, older cars in the past and up until owning these two GM cars, have not had problems with them. Any input on this is greatly appreciated.

@cleighton, my comment is not about the quality of Bosch parts . . .

I recently worked on a GM V8 truck that had insufficient upstream O2 sensor activity codes.
The cause of those codes was an exhaust leak ahead of the sensors.
After repairing the leak, the sensors started switching normally.

As for spark plugs, I always put in the ones called for in the owner’s manual.
I have never had a problem doing it that way.

FWIW . . .

I’ve used Bosch plugs in GM cars with no problems ever surfacing. As a matter of fact, my oldest son’s Camaro has a set of Bosch Platinums in it right now and they’ve been in there about 20k or so miles.
Like db4690 I usually stick to what the manual calls for; with a few exceptions now and then.

As to O2 sensors, keep in mind that the original GM sensors are not made by GM. They’re farmed out like just about everything else on a car and while I do not know who the supplier for GM is, it could very well be Bosch.
I’m pretty sure Bosch has a huge plant in Georgia or the Carolinas where they produce millions of O2s every year for just about everyone on the planet.

A late uncle of mine worked for Bosch as a foreman for about 40 years and he would have likely known the answer to that question.

When I see a car in for random misfires and I also see Bosch Platinum spark plugs installed I recommend replacement of the plugs using the OE plugs. I’ll of course diagnose any other issues present but won’t guarantee a satisfactory outcome until the Bosch Platinums are out of the picture.

I’ve had dozens of idle quality complaints and random misfire complaints that I was unable to account to anything other than the plugs. You couldn’t give me a set of those.

@asemaster, what do you do when the Bosch Platinum plugs ARE the OE plugs?

If you dont like Bosch plugs try NGK plugs. I find these better than Bosch but thats my honest opnion.

@db4690, I’d use them if they were original equipment but I don’t know of any cars that use those from the factory. I assumed the original poster was talking about the aftermarket Bosch Platinums that you get at the parts stores. As for me, I can’t “try” different kinds of spark plugs to see which ones work best. I always replace with the same brand and type the car came with.

" I always replace with the same brand and type the car came with. "
I’ll Drink To That !
It’s Chevrolet. Think AC Delco.

CSA

I’ve never had good luck with Bosch spark plugs, way back in high school I had a 1992 T-Bird SC. It came time to replace the factory spark plugs, at the time Bosch Platinums were all the rage so I decided to give them a try. The car ran like crap, uneven idle, minor hesitation, etc. Tried new plug wires, new distributor cap, new distributer rotor, even a new coil, still had the problems. Finally I replaced the Bosch plugs with a Motorcraft plugs and it ran perfectly.

I’ve also had good luck Champion, NGK and Autolite spark plugs.

I’d also say I’ve had poor luck with Bosch Platinum plugs. I’ve had two sets on two different cars, and on both, they had an uneven idle and occasional hesitation. After replacing them with Champions or Autolites, the problem went away. I did find out later from multiple sources that my Chrysler vehicles seem to like the cheaper plugs better.

As is the case with many other parts, if there were really a big difference among brands, the marketplace would sort it out pretty quickly.

That being said, there have been some rumblings of discontent on the auto enthusiast forums since Bosch was purchased by the Chinese. Call me prejudiced, but if the Bosch box says Made in India or Made in China, I ask what other brands they carry.

As for the parts mentioned here, I have never heard a complaint from a user of the proper spec NGK (NTK) or Denso spark plugs or oxygen sensors.

These are some great responses, and I agree with most that after having the issues with misfiring caused by non-OEM plugs that replacement parts should be the same or better than OEM. Unfortunately I must have forgotten about the plug issue when I ordered the Bosch O2 sensor. FYI, for those who mentioned exhaust leaks possibly causing the O2 errors, I just recently replaced the resonator and at the same time, did a complete check of the exhaust system. I don’t believe it is leaking anywhere else and I’m still quite confident that the sensor just doesn’t want to operate as it should in my GM vehicle.

@cleighton

So your exhaust manifold gaskets and exhaust manifold flange gaskets are definitely up to snuff?

I believe your original O2 sensor may have been manufactured by Denso.