check engine light?

Is there a way to get codes from the computer in a Chevy? I have seen the posts on how to do it if you have a Buick and the fancy digital HVAC system...

The light has come on a few different times, shutting off and restarting the car turns the light off. Seems to be running/driving just fine.
After I put the car back together the other day and drove around the light came on and the electric fan seemed to be constantly on. Shut the car off, restarted and the light was off and the fan was off. The fan does cycle on and off as needed otherwise. Wife said the light came on again today, she shut it off and restarted with no light on.

Looking at getting some sort of code reader or ALDL to USB setup. What are the current recommendations?

I see over on the Impala site talk about using EEHack and a small dongle like this:

https://www.ebay.com/itm/CP2102-FTDI-USB-3-3V-5-5V-to-TTL-Serial-Adapter-w-cables-for-Arduino-USA-Seller/133321753393

That is indeed the best way. A laptop, USB/ALDL Cable and eehack.

aldlcable.com is a good way to get a complete cable that just plugs in. The link that 94Woody posted is good; you can also get this one and solder it to the back of your ALDL port. USB cable for direct wire.

And yes, get really good with eehack. these cars are 25 years old; you'll need to get used to what the data SHOULD be so when anomalies show up you can quickly discern them.

I picked up a FTDI serial adapter and ALDL connector and made my own cable/dongle setup. I had to find a mini usb cable in the house to connect to the laptop.



I started up scan94/95 and connected to the car and started seeing info.
It shows me three DTCs:
15 Engine Coolant Temperature
32 Exhaust Gas Recirculation
48 Mass Air Flow sensor

When the check engine light comes on the electric cooling fan turns on, so I am assuming that is because of the ECT sensor... Is this the sensor in the water pump?

Otherwise I don't think there are any drivability issues.

The sensor in the water pump is for the PCM. The one in the cylinder head is for the gauge on the dash.

If I remember correctly anytime the CEL illuminates, the fans come on. Someone will correct me if wrong.

Looking at my FSM.

Code 15 is for the sensor in water pump. They are notorious for bad connections at the plug. You can buy a new sensor that will come with a new pigtail. This normally takes care of the issue.

Code 32 is of course related to that. The PCM is not seeing at least a 1.3kPa change in the MAP readings when it commands the EGR "ON". Can be cause by plugged passages, exhaust leaks and vacuum lines.

Code 48 is another obvious one. Problem in the MAF itself or the wiring.

I can take pictures of the troubleshooting pages if needed.

94Woody wrote:

The sensor in the water pump is for the PCM. The one in the cylinder head is for the gauge on the dash.

If I remember correctly anytime the CEL illuminates, the fans come on. Someone will correct me if wrong.

Looking at my FSM.

Code 15 is for the sensor in water pump. They are notorious for bad connections at the plug. You can buy a new sensor that will come with a new pigtail. This normally takes care of the issue.

Code 32 is of course related to that. The PCM is not seeing at least a 1.3kPa change in the MAP readings when it  commands the EGR "ON". Can be cause by plugged passages, exhaust leaks and vacuum lines.

Code 48 is another obvious one. Problem in the MAF itself or the wiring.

I can take pictures of the troubleshooting pages if needed.

The fan coming on makes sense to me as a sort of fail safe keep the engine as cool as possible...


Wondering how long codes stay stored in the pcm?

When I did the Opti overhaul and whatnot I started the car without the MAF connected. That was maybe a month ago.

I am going to replace the temp sensor and then look into the other stuff.

I believe the codes stay in the computer for 50 start cycles.

if Scan9495 doesn't have the ability to clear the codes, eehack does. The MAF code might be old.

I haven't used Scan9495 in ages but I know eehack has the ability to monitor data. I'd watch the MAF and coolant temp inputs and see if there's anything weird happening. One of my wagons would have an intermittent open circuit on the coolant temp sensor which made the car jerk at random times.

Don't replace the coolant temp sensor - unplug the connector and look for corrosion. I used a salt/vinegar solution to remove corrosion from mine, then sprayed it with CRC battery terminal protector to guard against future corrosion.

Code 32 might be from the EGR valve being clogged up, or from the threshold being set too high by GM from the factory. You can check EGR function in two steps. First, start the car, then using your fingers, manually force the EGR diaphram open. If it opens and the engine starts to run worse, then the system is working properly. Shut the car off, unplug the vacuum line, push the valve in and hold your finger over the vacuum port to seal it. If the valve stays open, it's still good.

If all those EGR tests pass, then the threshold in the PCM programming is set too high and the code is a false alarm. Since you have a data cable, I can fix that in the tune for you if you want. Send me a PM.

Thanks for the info and things to check and test.

Not sure if scan94/95 can reset codes or not. I only used it for a couple minutes yesterday to see if my cable setup worked. I also have eehack but haven't used it yet...

Really appreciate the offer for some tuning help!

Eehack is THE program to use for this stuff. Clears codes and lets you watch LOTS of parameters.

+1 on EEHACK, definitely clears the codes, used it ALOT when I was having stalling issues.