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OBDII Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Wed, 15 Nov 2006 05:31:26
In Reply to: Re: Year and model?, DAO, Tue, 14 Nov 2006 17:54:53 Members do not see ads below this line. - Help Keep This Site Online - Signup |
Being a '97, you need either an ISAT, TECH II, or OBDII reader. The first two are a bit pricey, but the last one is available at any big chain autoparts store. Get yourself down to the local Autozone or Pep Boys, and read out the codes (connector is on the bottom of the steering column, covered by a cap). You'll only get the generic codes, not the extra Saab-specific codes that add a little more info. But it's a very good start.
Since the car is running fine, it is most likely a sensor that the engine control can work around. Examples would be the coolant temperature, or throttle position sensor. Lose the MAP sensor, and the car won't run well. Lose the coolant sensor, and the engine can handle it just fine. Another one would be any number of Purge Valve or ECLD faults - that's the evaporative emissions system. It works by capturing the gas tank fumes in the charcoal canister, and then sucking them (via a valve) at the proper time into the intake manifold. When the valve opens, the ECU assumes the engine will behave a little different (extra air and fuel will do that). If the engine speed change isn't as expected, it assumes the valve is bad. But it would also catch a loose gas cap/bad gas cap seal, or many vacuum leaks.
As an example, I got a CEL on my wife's '97 last week. A quick visual inspection showed that one of the wires to the throttle position switch had broken. The only symptoms were the AC didn't work, and the throttle seemed a bit touchy. But the temperatures were such (50's, F) that one doesn't notice AC, and the wet roads made the throttle touchy anyway. A quick wire splice, remove the battery cable for a minute, and all was well.
I would do a visual inspection of the engine bay. Follow all wires to sensors, and make sure they are hooked up and the cables seem intact. Check all vacuum hoses, especially in the area of the intake. One place to check carefully is the hose/valve from the valve cover to the intake. I've seen that one way valve crack with age, and that vacuum leak can cause a CEL. Remove the right front turn signal assembly and look in at the top of the charcoal canister - make sure the hose is still attached. And if none of those show up a problem, a quick spin down to Autozone or the like will get the codes.
Once you get the codes, check back to the BB. The codes are only the start of troubleshooting, not the final answer. Some faults are clear - a bad Throttle Position Sensor (TPS) will give a TPS code - but is it the sensor, a broken wire, or a bad connection at the ECU? Others are less so - an O2 sensor failure usually isn't the O2 sensor. A vacuum leak that causes a lean condition can generate an O2 sensor fault. A blown O2 sensor heater fuse will generate an O2 sensor fault. Replacing the sensor is the wrong answer in both cases.
posted by 192.249....
, Tue, 14 Nov 2006 06:04:56, Wed, 15 Nov 2006 05:31:26 <-- Viewing This Message
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