Hello all. Corvette newbie here. Picked up a 1995 auto a couple months ago. Anyways I had lean faults and rough running. I replaced both 02 sensors and the car ran smooth but somewhat sluggish. Still had the lean faults return. Someone recommended replacing the knock sensors. So I replaced them and apparently got some coolant into the 02 sensor connectors. When I turned the key forward to clear the faults for a test drive the fans started running and I no longer have ECM communication. I cleaned all the connectors and checked every fuse I could find. Is there a chance I spiked the ECM by getting coolant on the 02 sensor connectors and turning the key forward? After a week I'm at a loss. Any help would be appreciated. I'm not off to a good corvette start here.

 

not sure if related to your issue but...

did you use ac delco o2 sensors? (pref. new old stock made in usa) or off-brand (like bosch?)

 

[QUOTE=dizwiz24;1595453498]not sure if related to your issue but...

did you use ac delco o2 sensors? (pref. new old stock made in usa) or off-brand (like bosch?)[/QUOTE.

Hello. I didn't use AC Delco but the repairs were done about a week apart. The car ran ok just set the lean DTCs every 100 miles or so. The trouble started when I changed the knock sensors

 

Yes, there is a chance of that if there was enough coolant to cover voltage and ground, coolant has some conductivity, but I'm not sure I'd put my money on that as being the problem.

Are any codes being thrown or are the codes indicating the lost of ECM communications?
http://tech.corvettecentral.com/2011...trouble-codes/

 

Good morning. What's happening now is when I plug in my scan tool it lights up so I didn't down the power supply to the OBD it's just when I try to access engine it won't talk anymore

 

What are you using for a scanner? BRAND and MODEL!!

 

I think your ECM is bricked, but I seriously you caused it by getting coolant on the O2 sensors. Those things are expected to get at least a little wet from time to time, and on my car with long-tube headers they are down by the road surface and get sloshed by any water on the road. But in my experience, if the fans come on any time key is ON, then your ECM is no good anymore.

 

Hi thanks for your reply. So I was outside checking things and I got the ECM to talk. I may have had dirty connectors at the DLC. I have a hard code 43 ESC module or sensor circuit problem. I'm using a snap on solus pro scanner. Here's the odd thing. I had this fault before my fan issue off and on along with the lean codes. The O2 sensors smoothed the car out and got rid of the 43. So the 43 may have been an unrelated already there issue. Not sure. I went through everything I did relating to the knock sensors. Cleaned connectors etc. still fans are stuck on. Is the ESC module the optispark unit on these cars?

 

By ESC, you are referring to an ignition module I believe. No, on these cars the optispark module provides a signal to the engine for the crank position, but there is a separate Ignition Control Module (ICM) mounted to the passenger-side front of the cylinder head, on a bracket along with the coil. I guess it's possible that it could be causing "sluggish" behavior, but that's not the typical failure mode for these. They usually basically won't fire the coil at all (sometimes only when they heat up). If all plugs are getting fired every rotation (i.e., no misses) then I doubt your ignition system is the culprit.

If you are still getting lean codes, that could cause the sluggish feeling. It's probably a good idea to try to log the engine running and see where the A:F ratio is along with the ignition timing. It still bothers me that your fans are running all the time. It makes me think the ECM is no longer controlling them for some reason.

 

Yeah me too. I'm almost feeling I need to send the ECM out and have it fixed. The car prob has 2 issues. I'm a VW tech and whenever you lose ECM or it's damaged your fans come on and won't turn off. Maybe GM is different but ford does the same

 

These GM ECMs do the same thing, at least 94-96. I imagine many others, too. I have two bricked ECMs in my garage and they both run the fans full-time. So I have the evidence!

BTW, are you sure the knock-sensor module is installed in the ECM? There's a little plate you remove to access it. I once put an ECM in my car without the module by mistake, and the car was very sluggish. I think the ECM defaulted to some minimal timing advance strategy. So double check that. That won't cause the fans to stay on though.

 

OP - you mention you've succeeded in getting the PCM to communicate again with your scanner. I think the "bricked" assumption is maybe a bit "rushed". A GM '95 with certain DTC codes will turn on fans.

You've never mentioned all of the DTC that you have. A '95 I believe should display I believe a combination of OBD1 and OBD2 DTC. Can you supply a list of the DTC that the scanner has confirmed. How have you cleared/reset the PCM in the past?

 

I've always just cleared the codes using the scan tool. I didn't know there was another way. From the time I bought the car it's had lean faults bank 1&2 and occasional code 43 ESC module. But never any fan running issues. That happened after the knock sensor/coolant on connectors deal.

 

Does anyone know of these companies that you can send your ECM out to be repaired in these situations? I was looking on eBay for used/reman ECM sand saw A1 Cardone offers a ECM fix service for 170. If anyone has a used one for sale the part # is 16181333. Heck I don't even know in 95 whether these ECMs are plug n play 😐

 

Larry, I have seen good reviews for SIA Electronics. But I don't know that you're quite to that stage yet. I am still trying to figure out how the knock sensor job could have possibly caused the fan issue. I am assuming drained coolant from the sensor ports in the block and maybe also from the petcock at the bottom of the radiator. In either case, it's pretty hard to get coolant on anything delicate. Again, all that stuff at the bottom of the engine is made to withstand weather, so a little coolant shouldn't short it out.

So now that you've cleared the codes, are you getting any new codes reset at all? Will the engine start at all?

 

Hi Matthew, the car starts and runs smooth. The check engine light comes on right away and the fans start. When I clear the code 43 the fans turn off for a second then the DTC light comes back on and the fans start running again. I don't want to downplay how much coolant got into the driver side 02 connector. It was a lot. I didn't realize how much until the malfunction and when I unplugged the 02 connector it was full of coolant. I assume these cars are getting older and the rubber seals that keep moisture out may not be as effective as they were 20 years ago.

 

I still don't see how the O2 sensor connector having coolant in it could do this, especially if there is no code for O2 sensor malfunction being thrown. There just isn't that much voltage or current being supplied to the O2 sensor that it should be able to blow things up with a short. Here is a thread on Code 43 that indicates it could be one of the knock sensors itself causing the problem, or the knock sensor module plugged into the ECM. Here's another thread that indicates the same, and also hints that the fans come on automatically with that code. That would make sense as a failsafe against more knock, since a hot engine tends to knock more. I would do some more searching on "trouble code 43 LT1" and read up.

In your car's case, code 43 is for the knock sensor circuit, not the ignition control module. That thread I linked above as well as the factory service manual for my 96 (which is a bit different in being OBD2, but I believe the knock sensor circuit works the same) both indicate that the ECM will pull timing if there is too little or no voltage from a knock sensor. Hence, if you installed a knock sensor that is bad or is the wrong kind for the engine, that may be your whole problem. Or, maybe the knock sensor got too much thread sealer on it and isn't grounded to the block well enough. Or maybe the knock sensor module in the ECM actually went bad, although this seems less likely.

You certainly have the option of putting the old knock sensors back in. I doubt they were malfunctioning in the first place, since they shouldn't cause a lean condition.

 

Thanks for the tips! I didn't save the old knock sensors and they weren't OEM so I'll pick up a set tomorrow at the dealer and start from scratch. You're correct as these aftermarket units didn't have any thread sealer on them to begin with. One thing I don't get with thread in knock sensors is the block threads are so gritty even after cleaning them you exceed the torque spec before they are even tight. I haven't begun to address the lean faults other than a new fuel filter and a MAF that was on its way out being the original one. I'll fix that later. For now I need to dump the 43 code and stop the continuing fans running as with my luck they will burn up from running all the time. I'll at least start with OEM knocks and work my way back.

 

Maybe you do the checks before you buy more. If all you've got is the DTC 43 here's the checks from a '95 FSM








You likely have all-data or something available from your work maybe?

 

Hey! Thanks for the trouble tree. I will have all data next month. Right now I have just German car data as that's what I fix for a living. Believe it or not a lot of times it's harder to fix your own car because I'm always fixing someone else's and have to work my own car in at the end of the day. Then focus can be an issue.