"seervice engine soon " light

[Scott V.]

recently purchased 1999 tahoe lt, 57,000. 5.7 auto, 4wd. Nice truck. Installed airraid intake, cat back duals. Received O2 sensor codes on computer. reset then wnet a few weeks, they reappeared. I replaced both with Bosch brand O2 sensors. Code cleared, two day slater mass air sensor coded, replaced Mass air sensor. code went away for month, today it was come back, light stays on. All suggested tiems checked out ok. How can I reset light wihtout a computer and most major question, what else could be wrong with this trucK? HELP!!!!! thanks in advance for your answers.

[GMMerlin]

First off, you need to do a little diagnostics...
Just because you get an O2 sensor code doesn't mean the O2 sensor is faulty...it may mean that the PCM sees a voltage range outside what is expected and the sensor cannot compensate for it.
If the light wasn't coming on before your modifications then that is where I would look...maybe something you changed is causing the problem... I would say if you do some heavy modifications and don't change the PCM program to match, that may be your problem.

[Scott V.]

Originally Posted by Scott V.

recently purchased 1999 tahoe lt, 57,000. 5.7 auto, 4wd. Nice truck. Installed airraid intake, cat back duals. Received O2 sensor codes on computer. reset then wnet a few weeks, they reappeared. I replaced both with Bosch brand O2 sensors. Code cleared, two day slater mass air sensor coded, replaced Mass air sensor. code went away for month, today it was come back, light stays on. All suggested tiems checked out ok. How can I reset light wihtout a computer and most major question, what else could be wrong with this trucK? HELP!!!!! thanks in advance for your answers.

Reply: beside the Air raid intake and the cat/back duals here has no other mod's to the engine. I bought a computer analyzer today and reaad the codes. they were listed as "Left bank too lean" and another read "right bank too lean". the most recent SES light was illuminated right after a short 15 minute idle in a parking lot. then this morning onduring my 18 mile drive to work the light went off? the location I purchased my computer from suggested that the muffler may be too open to support the current electronic programing. My experinence in working on older cars has corrupted my view here. The older carburated engines loaded up while parked not leaned out? thanks again for the help alrady plese , more feedback is appreciated.

[Scott V.]

oh by the way Merlin, whats a PCM?

[Scott V.]

Originally Posted by GMMerlin

First off, you need to do a little diagnostics...
Just because you get an O2 sensor code doesn't mean the O2 sensor is faulty...it may mean that the PCM sees a voltage range outside what is expected and the sensor cannot compensate for it.
If the light wasn't coming on before your modifications then that is where I would look...maybe something you changed is causing the problem... I would say if you do some heavy modifications and don't change the PCM program to match, that may be your problem.

Thanks Merlin, I appreciate you response. The only mods I have performed to this tahoe are the listed ones ie: the airradi intake and teh duals. The computer codes revealed today were two seperate ones reading " left bank too lean" and " right bank too lean" . The light came one immediatly after a 20 minute idle session in a parking lot. I would assume that the engine would load up rather then lean out during a time as such? Whats is a PCM and how would I get it reprogramed? Your info is greatly appreicated thanks again.

[GMMerlin]

the PCM is the Powertrain Control Module or as everyone knows it "the computor"
It is calibrated for the stock set up in your vehicle. It reads the sensors to determine if the engine is running at peak efficency...if you have modified the engine to take in more air and scavage the exhaust faster, the PCM does not reconize the change and from its calibrations believes something is wrong...
A hypertec or some other aftermarket program may help