emission sensors / battery diconnect

Greetings!
I've been fighting with my 97 Grand Caravan 3.8 over an intermittant stalling problem. I had the battery out this weekend but need to get a new emissions sticker so here's my first question:

How long after a battery disconnect does it take for the emission sensors to turn on? Is it a fuction of mileage or on/off cycles? Also, can they be turned on manually with a scan tool?

Thanks, TX

My 98 Caravan keeps stalling. After replacing the battery has the stalling stopped?

I took the battery out to check the grounds and splices that are underneath the battery tray.
By coincidence I needed to get my smog check and was told that it needs to be driven for a day for the sensors to turn back on after a battery disconnect.
I went back today (3 days and 50 miles later) and the sensors were still not on. I'm wondering if the stalling (which happens at least 2 or 3 times a day) is caused by the computer losing power.

A little confused as to what you are talking about. All the sensors "turn on" when you start the engine. They are never "turned off" unless they malfunction. Normally, the failed component will generate a code and turn on the Service Engine Light (SEL). Unfortunately, that's not always the case.

Could the smog techs be seeing a Service Engine Light (SEL) on the dash? That is an automatic fail. It may or may not reset after a number of key cycles (50?). They may be telling you to drive till the light resets itself. If the SEL is on, take it to Autozone where they will connect a scanner and read the error code that is turning the light on. They can reset it. It's free.

You said, "I went back today (3 days and 50 miles later) and the sensors were still not on." What is telling you the sensors are still "not on"?

The Powertrain Control Module (PCM) is the computer that controls all engine functions. It goes through a learning process conditioned by various sensors as you drive. This data is stored and and continually updated. I believe this data is erased when you disconnect the battery. Your engine and computer then "relearn" once the battery is reconnected and you drive along. This may be what someone is refering to when they tell you "drive it for a day". Same for the Transmission Control Module. If I'm knocking on the wrong door let me know.

I should have used the phrase on the report which is "not ready"
The SEL is not on and passes all checks.

Here's a summary of the report:

SEL check pass
SEL on run pass
ready result FAIL
fault code reset pass
SEL status pass
DLC result pass

The following are shown as "ready"
misfire ready, fuel system, comprehensive component

These are shown as "not ready"
Catalyst, EVAP system, O2 sensor, O2 sensor heater, EGR system

Maybe they will become "ready" after the computer gathers enough data?
So I guess what I'm wndering is How long does it take for the computer to relearn?
Thanks, TX

OK. You're getting this info off a smog check report which I'm not all too familiar with. I would expect the relearn procedure wouldn't take more than 2/3 days of driving.

Found this article that touches on your issues: http://www.aa1car.com/library/ic50234.htm Scroll down to "ready or not". Based on this we need to find out exactly what driving conditions the PCM is looking for in order for it to "relearn". Might give the dealer or local shops a call and see if they know. As a last resort, if this doesn't clear up you may need to have the PCM reflashed by the dealer meaning, reload it's basic programming.

Thanks for the link. It was a good article and I looked at some other articles on that site too.

I've been wondering if this is a symtom of the stalling problem. Perhaps when it stalls the computer loses its data and has to start the learning process over? Since you're on the line, I'd like to get your thoughts about the stalling problem.

I kept a log for a week to track the stalling incidents:
On 5/8 cold starts it stalled exactly two minutes after, then restarted fine.
the other 3/8 no problem.

When hot it would stall between 2 and 15 minutes after starting about 50% of the time.

On long road trips, it will drive 100-200 miles trouble free, then stall once or twice after stopping.

It always restarts, and restarts on its own if cruising over about 20 mph.

Thanks again, TX

Thanks for the link. It was a good article and I looked at some other articles on that site too.

I've been wondering if this is a symtom of the stalling problem. Perhaps when it stalls the computer loses its data and has to start the learning process over? Since you're on the line, I'd like to get your thoughts about the stalling problem.

I kept a log for a week to track the stalling incidents:
On 5/8 cold starts it stalled exactly two minutes after, then restarted fine.
the other 3/8 no problem.

When hot it would stall between 2 and 15 minutes after starting about 50% of the time.

On long road trips, it will drive 100-200 miles trouble free, then stall once or twice after stopping.

It always restarts, and restarts on its own if cruising over about 20 mph.

Thanks again, TX
Would not hurt to put a fuel pressure gage on and watch the fuel pressure on cold starts for a few minutes.

I'd be more willing to bet that he has a bad o2 someplace. No such deal as " Hey, I need a day or 2 to get my crap together". As I said, I bet an o2 is bad. Get it scanned. Check around most shop will charge a small few to check it out with a scanner. I guess you could go get your own.......If you have that kinnda cash layin around.

After many weeks of checking everything, I bought a new engine computer and the problem is solved.