HI All. I'm New Here and I'm very frustrated with this Bonneville

It'* a 1989 Bonnevile LE w/ 3.8 V6 Engine.

My service engine soon light has been going on and off intermitently for a few months. I've reset it, fixed things, etc and nothing works. Here'* what'* up.

The following codes are pulled when i check them.

16 - System voltage out of range
21 - Throttle Position Sensor Voltage High
22 - Throttle Position Sensor Voltage Low
23 - MAT Sensor / IAT Sensor
43 - Low Voltage at ECM / Knock Sensor

once in a while i'll get this code ALSO

15 - Coolant Sensor.

These codes always pop up (with the exception of code 15 which is less often) when i check the codes. I've replaced the TPS and the Service Engine soon light just stayed on. I've replaced other sensors and the same thing happens. All sensors and everything are back to what were originally in the car when i bought it because new ones make the SES light stay on.

Some things the car does...

when the SES light comes on... sometimes it will just run normal, sometimes it will idle very low (to the point it almost kills off and a couple times it did kill off)
when the SES light comes on... sometimes it runs at high idle (around 2100 rpm) and it shifts pretty hard from park to drive, drive to reverse, etc.
when the SES light is on, the car sometimes runs normal, sometimes it shifts hard, sometimes it feels like the engine is choking.

These are the problems and symptoms....

I'd like to know if anyone has any ideas on what else to do. When i reset the computer (disconect the battery for 10 minutes) the light stays off for a few hours and then turns back on. Sometimes the symptoms happen alot, sometimes they dont happen too often. It'* very confusing and frustrating. A mechanic will charge an arm and a leg to start the diagnostics work and another arm and leg to continue the work which i don't want to do.

Any help will be appreciated, and thanks.

I'm not sure, but it sounds like you may have low voltage when the SES light comes on. I would check your system voltage when the SES light comes on.

You may have a bad battery, alternator, or just poor or dirty connections. You can also try cleaning the battery cables and terminals with a wire brush.

Is there a way to check the alternator w/o taking it off. It still charges good cause the car does not stall from dead battery. All lights and radio still work when it happens

i'd check the connections before i started ripping the car apart
but you're going t have to pull the alternator to have it checked
AutoZone in my area does it for free they probably do in your area too

You can check low system voltage with a voltmeter with everything still together. Check it at the battery terminals. But you want to check it when the goofy conditions occur.

Anybody know where to get free diagnostics flowcharts or does anyone have any that could help... please let me know. My car has been acting up for a while and I think it'* time to fix it.

Have you checked for a bad ground to the ECM? If not, try there, as these may all be caused by a simple problem the ECM is trying to fix!

Thanks for the insite guys... hopefully this works... i'll let you know how it all ends up. Any more info would be greatly appreciated.

thanks

It'* been raining around here lately and my car has been kinda sluggish at starting. Have to turn it over once or twice and then the next time... it just fires up... could this be another problem (damn bonnevilles... always a problem... there just nice cars)

It still sounds like battery - alternator problem. Do you have a Wal*Mart near by they should have a unit that will test you battery and alternator without taking it out of the car. The one I work at has this unit and they test cars for free. They will hook it up and go through a couple of things like turning head lights on, rev-ving up the engine, turning all accessories on. I should tell you what is wrong with it. The bad thing is if it is a bad alternator you are probably going to have a bad battery because the car has been putting too much stress on the battery since your alternator has been messing up. You can do a quick check by getting a multimeter and checking the voltage at the battery post it should at least be 13V like jr'* 3800 wrote.