Check Engine Light after Aftermarket Exhaust Installation

[Tred]

BOOO!!

I just installed a Magnaflow system for my 2.7L, and the demonic Check Engine Light (CEL) came on. I haven't gotten anywhere to get the code pulled off, but I have heard that aftermarket systems can cause the air/fuel to be too lean, and also sometimes, because there is not enough back pressure in the exhaust, the O2 sensors would not work properly....

Here's what I have:

2002 2.7L @ 37,000 miles
Volant intake system installed around 33,000
Magnaflow catback system installed just recently

The intake system did not cause any trouble at all. No CEL, except for when I forgot to plug the O2 sensor back on.

Magnaflow however, caused a CEL about a week after I installed it. Installation was done by myself (it was very easy, and it sounds nice!), and I believe I've done everything properly... except for when I forgot to put the gasket for the O2 sensor mount on the new system AFTER I got everything done, and got my garage cleaned.... At least I noticed the little gasket sitting on my original exhaust. I did reset the computer by unplugging the battery during installation.

Anyhow, like I said, I haven't pulled the codes yet. I need to go do that soon, but my question is, do aftermarket systems really cause the CEL to come on? And if it's the air/fuel mixture that is too lean what can I do to fix that? What if it's the back pressure? Are there other reasons why the CEL would come on, other than failures not related to the modification?

[Brian R.]

One possibility it the new intake system could have contaminated the MAF sensor in some way - taking this long to do it.

Don't guess, get the code

[Tred]

P0136 O2 Sensor Circuit Malfunction (Bank 1 Sensor 2)

A $120 piece....

I wonder what really is going on. I followed the cable from the O2 sensor a bit, and well, it goes into the truck less than 2 feet from the sensor, and I have absolutely no clue how to replace that.

Even if I replace it myself, god only knows if replacing the sensor would fix the problem.

I'm going to take her in.

[MachoTACO]

My Tacoma is a 2004 and my check engine light came on at 9,000 miles I took it down there and they fixed it for free it was some cap that came off and they replaced it. It was tripping the air/flow sensor.

[Tred]

Hmmm, well I'm over 37,000 on a 2002. When I call tomorrow, I'll ask if the O2 sensor is covered by any of the warranties I still have.

[Tred]

$90-150 for labor. She also said that "I'm on my own to get the full diagnostics, if this doesn't fix the problem." Looks like I'm in the shitter.

Well, I'm just going to have them check the O2 sensor then. I'll figure out how to change the sensor myself if it indeed is faulty. Anyone have experience in this?

[Tred]

I got my ODB Scanner from http://www.ghg.net/dharrison/ in the mail today. I got it hooked up, and well, the O2 Sensor in question is indeed acting weird.

The voltage would quite frequently drop to 0.00v, and stay there. I haven't confirmed this fully, but road bumps seem to kick it in and out of this. When the sensor is creating voltage, it would stay around .3v unless if I gas it at 70%+ throttle.

I will be changing the exhaust gasket and O2 sensor gasket Tuesday, when they get shipped, then if necessary the O2 sensor.

I hope the wiring between the sensor plug to the ECM is fine. If it is, I really would have to take it to the dealer.

[Tred]

Exhaust gasket and O2 sensor gasket replaced. No change. Still triggering P0136. Will be replacing the O2 sensor tomorrow.

[hurdaddy]

Tred, Did you ever find a fix for your check engine light? I drive a 2000 4.4 w/ a 2.7L and have a similiar problem. Any info you can give would be muchly appreciated.

[Tred]

Try...

http://www.customtacos.com/ubbthread...&Number=362317
http://www.customtacos.com/ubbthread...&Number=439486