I'm constantly getting a code 33, and was wondering what this could mean?

I've heard its bad to start the car while the paper clip is in the 1-2 pins to check codes, but how bad is it? could i have fried my ECM? is that why the code is staying?

The reason i ask is that I just replaced my MAF sensor and its still giving me the code. People shrug and tell me it takes a while for the ECM to re-learn or whatever, but taht doesn't sound like it makes sense.

 

What year car? And starting the car with the diagnostic pins grounded just forces it into the "limp home" mode.

When driving the car and the check eng light comes on does the engine do anything like sputter, put out black smoke, die or run rough? If so, when you restart the car is the light still on? If so, does the car appear to run normally?

Some things to check, check the connector to the MAF sensor, make sure none of the female pins have been distorted.
If it is an early model, try swapping the MAF burn off relay and the fan relay (they are supposed to be the same relay). Check that the power wire going into the MAF is at 5 V. Check the throttle position sensor voltages.

If everything checks good, call GM and see if there was a service bullitin for oyur car for a false code 33 or 34. There was one for the '85's that changed the PROM (don't ask me how long I fought that one)


~M~

 

TD,

STARTING the engine with the ALDL diagnostic request pin grounded can cause damage to ECM the firmware. It doesn't always cause damage, but it CAN. If you've done this, disconnect the battery for about ten-twenty minutes to make sure the BLM tables and all RAM is cleared.

Grounding the pin AFTER the engine is running is not a problem. This will force the Field Service Mode, not Backup Fuel. (To force the Backup Fuel Mode AFTER the engine is running, insert a 3.9K ohm resistor between the pin and ground.)

You can ground the diagnostic request pin and turn the ignition ON (without cranking) with no problems, of course.

As for your '33', do as Morley suggests - check the connectors and relays first.

A TPS voltage that is set too low can also caause a '33'. You really need to be as close to the 0.54VDC level as possible.

You can also get a '33' if the distributor reluctor is failing or the distributor reference pulses are not getting to the ECM.

Another possibility is a poor ground at the ECM or engine wiring harness. The ECM references all input signals to the ECM ground, and if there is resistance in the ground path, the signal will appear higher than it should.

For reference, what year is your car, and what sorts of modifications (if any) have been done?

 

its an 86 iroc with a 305 TPI, and no mods yet.
Ok, I'll try to check that stuff, but i don't konw where most of it is. I'm gonna take a look at the TPS and see what I find. one weird thing it does is when im idling down the street not giving it any gas, the RPMs drop suddenly about 500 rpm and then raise back up. could something be loose thats throwing the TPS off?
Sorry if I sound like a doofus, I don't know these motors too well yet.

 

well i just got through cleaning out the whole TB, and I cleaned up the IAC too. I didn't have a voltmeter, so tomorrow I gotta get one and re-adjust the TPS, but it seems to be idling erratically still.
I tried setting minimum air, but it was hard cause it kept moving all over the place. I wont make any assumptions until I can re-adjust the TPS.

It stays running better, but the SES light is still on. It's on all the time when the car is running, it never goes away. i reset the ECM too.

The only other thing I can think of is I may need a new MAF connector pigtail.

Where would I find the distributor reluctor, and how would I test it? before I mess with that, I'm gonna re-adjust the TPS voltage, but just so I can check if it doesn't go away...


Thanks guys. I'm already learning!

 

Will look in one of my manuals for this problem, they have good troubleshooting trees, give a good place to start looking.

~M~

 

If your MAF and the connections are good, I'm betting on a TPS that is set too low. Don't set the minimum air position by the tachometer on the dash. They are not accurate enough to use as a diagnostic tool, just a reference.

 

well I got my TPS to .543 volts and my minimum air to 700 or so. The SES light is still on, so next is a MAF connector. I just gotta find a junkyard around that has one. the car is running much smoother though, even with the SES on. I'm going to check which codes its spitting tomorrow morning, although I'm sure its still a 33. It never went away.