1981 ECM Code 15
Thread Starter
Instructor
Joined: Oct 2009
Posts: 165
Likes: 1
From: Stanley NC
1981 ECM Code 15
Hope all are doing well. My '81 is giving me a temporay check engine light about 2 minutes after start up and this come up to be a Code 13, Oxygen sensor but the light goes out in about a minute. But 5 minutes running the check engine light comes on and stays on and gives me a Code 15, Coolant Sensor.
Once these codes pops up the carb starts to run rich and the vette does not run likes she should. Engine temp is fine, normal so not affecting the engine temp, just the carb.
Thoughts, comments, suggestions? Waiting now to get the vette into the local shop to have him check it out if I cannot come up with solution. I have none of the meters to check the system as outlined in the '81 shop manual.
Second question, has anyone of you with an '81 bypassed the ECM system completely? I know this means a different carb and vac dist and then address the transmission lock up switch, anything else? I average only 10 miles to the gallon running 93 octane so wondering if this swap out would improve fuel mileage.
Once these codes pops up the carb starts to run rich and the vette does not run likes she should. Engine temp is fine, normal so not affecting the engine temp, just the carb.
Thoughts, comments, suggestions? Waiting now to get the vette into the local shop to have him check it out if I cannot come up with solution. I have none of the meters to check the system as outlined in the '81 shop manual.
Second question, has anyone of you with an '81 bypassed the ECM system completely? I know this means a different carb and vac dist and then address the transmission lock up switch, anything else? I average only 10 miles to the gallon running 93 octane so wondering if this swap out would improve fuel mileage.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,112
From: Crossville TN
Change the oxygen sensor, the coolant [temp] sensor, and the thermostat. Apparently, the oxygen sensor is starting to degrade, but not totally shot [intermittant light]. The coolant sensor is only checked after a period of time where the computer assumes that it is up to temp; since it is not, it throws a code and the ECL stays lit till the engine is again shut down. That problem could be due to a thermostat that is stuck open, a bad temp sensor...or both. If those devices are old, just change them out.
Thread Starter
Instructor
Joined: Oct 2009
Posts: 165
Likes: 1
From: Stanley NC
I started getting the Code 15 a week ago. Temp gauge still shows now as it did since I own this vette. From cold start temp goes up to 200/f and then drops back down to around 180/f and stays there unless in stopped traffic in hot temps then rises up to about 200 again.
Check engine light is like a clock, per the shop manual after 5 minutes of running if detected Code 15 will appear and like a clock 5 minutes it is on but temp has gone to 200 and then dropped back to normal.
Check engine light is like a clock, per the shop manual after 5 minutes of running if detected Code 15 will appear and like a clock 5 minutes it is on but temp has gone to 200 and then dropped back to normal.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,112
From: Crossville TN
180 deg is inadequate for what the computer wants. There should be a 195 deg. thermostat in the car. If a lower temp stat was installed, that is why you are getting the code. If lower than 190 deg, the computer will throw a fault and various parts of the system will not function properly and the engine management program will go into a 'default' mode instead of using actual data as it should.
Melting Slicks
Joined: Nov 2005
Posts: 3,322
Likes: 141
From: Green Valley Arizona
Two temp sensors; one on the driver's side in the head, other on top of the intake manifold. Right now I cannot remember which is which...easy to check though. With engine running, disconnect one of them and if the temp gauge reading goes either to zero or full hot, then that is the gauge sensor and the other one is the one for the computer.
If the computer thinks the coolant is cold, it will richen the fuel mixture.
I have a 180 thermostat but with an non stock EPROM so I have no problem. Having a 180 stat and the stock EPROM could be a problem as was stated.
If the computer thinks the coolant is cold, it will richen the fuel mixture.
I have a 180 thermostat but with an non stock EPROM so I have no problem. Having a 180 stat and the stock EPROM could be a problem as was stated.
Thread Starter
Instructor
Joined: Oct 2009
Posts: 165
Likes: 1
From: Stanley NC
Yes the sensor located on top of the manifold behind the air pump is for the ECM and has a black and yellow wires going to it. I do not have the meter or special tools to check this system out per the shop manual so now have car scheduled to go into local vette mechanic next week and he is going to check out entire ECM system and fix accordingly hoping to remove any other probelms or else consider swapping out carb and dist and doing away with ECM all together. Also brake booster replacement is schedule too.
My mechanic by phone feels 99% it is a bad sensor but also says the GM replacements comes with 2 white wires, not color coded so have to trace out the wires to ECM to get correct connection.
My mechanic by phone feels 99% it is a bad sensor but also says the GM replacements comes with 2 white wires, not color coded so have to trace out the wires to ECM to get correct connection.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Grand Sport & Grand Sport X Launch Alongside All-New 535hp LS6 V8!
Michael S. Palmer
5 Reasons Bad Drivers Crash & 5 Ways to Avoid a Costly Mistake!
Joe Kucinski
7 Bolt-On Upgrades From Extreme Online Store to Level Up Your C6 Corvette
Pouria Savadkouei
How Likely Are These Five 2027 Corvette Rumors to Be True?
Brett Foote
9 Best Corvettes You Can Buy for Half Price (& 1 You Should NEVER Buy!)
Joe Kucinski
8 Very Best Corvettes of Amelia Island 2026
Joe Kucinski
Top 10 WORST Corvette Engineering Failures of All Time!
Joe Kucinski
10 Records the C8 Corvette Generation Has SMASHED (& 1 Glaring Failure)
Joe Kucinski
7 Wildest Corvette Concepts Ever Made
Brett Foote
Drifting
Joined: Aug 2009
Posts: 1,635
Likes: 8
From: Enid Oklahoma
Hope all are doing well. My '81 is giving me a temporay check engine light about 2 minutes after start up and this come up to be a Code 13, Oxygen sensor but the light goes out in about a minute. But 5 minutes running the check engine light comes on and stays on and gives me a Code 15, Coolant Sensor.
Once these codes pops up the carb starts to run rich and the vette does not run likes she should. Engine temp is fine, normal so not affecting the engine temp, just the carb.
Thoughts, comments, suggestions? Waiting now to get the vette into the local shop to have him check it out if I cannot come up with solution. I have none of the meters to check the system as outlined in the '81 shop manual.
Second question, has anyone of you with an '81 bypassed the ECM system completely? I know this means a different carb and vac dist and then address the transmission lock up switch, anything else? I average only 10 miles to the gallon running 93 octane so wondering if this swap out would improve fuel mileage.
Once these codes pops up the carb starts to run rich and the vette does not run likes she should. Engine temp is fine, normal so not affecting the engine temp, just the carb.
Thoughts, comments, suggestions? Waiting now to get the vette into the local shop to have him check it out if I cannot come up with solution. I have none of the meters to check the system as outlined in the '81 shop manual.
Second question, has anyone of you with an '81 bypassed the ECM system completely? I know this means a different carb and vac dist and then address the transmission lock up switch, anything else? I average only 10 miles to the gallon running 93 octane so wondering if this swap out would improve fuel mileage.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,112
From: Crossville TN
Just curious, 81pilot. Didn't you state in a prior thread that you ripped that system off the car immediately after you got it? That would mean that you never ran it as the stock system to begin with. True or not? 
Drifting
Joined: Aug 2009
Posts: 1,635
Likes: 8
From: Enid Oklahoma
I may have said immediately, however, it took a while to gather the parts, so I drove it about 6 months or so. And all the way back from Arkansas the day I bopught it, so I think that was ample time to gain an informed decision as to what I wanted to do.... Why is it everytime anyone ASKS about pulling the computer system on an 81 you get your panties in a wad? Just sayin, I really don't care what people do with thier own car.....
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,112
From: Crossville TN
Just reporting what I've read from you in the past. Consistency is important to gaining credibility. And, I didn't indicate anything about the poster 'losing' the CCC if he wanted to...did I?
Melting Slicks
Joined: Jul 2005
Posts: 2,740
Likes: 3
From: Aurora Ontario
Yes the sensor located on top of the manifold behind the air pump is for the ECM and has a black and yellow wires going to it. I do not have the meter or special tools to check this system out per the shop manual so now have car scheduled to go into local vette mechanic next week and he is going to check out entire ECM system and fix accordingly hoping to remove any other probelms or else consider swapping out carb and dist and doing away with ECM all together. Also brake booster replacement is schedule too.
My mechanic by phone feels 99% it is a bad sensor but also says the GM replacements comes with 2 white wires, not color coded so have to trace out the wires to ECM to get correct connection.
My mechanic by phone feels 99% it is a bad sensor but also says the GM replacements comes with 2 white wires, not color coded so have to trace out the wires to ECM to get correct connection.
The only other possibility is low coolant. If the rad isn't full the sensor will malfunction.
O2 is plug anf play.
Both sensors are cheap and easy to replace. Both are critical for fuel/air mixture.
Jim
Drifting
Joined: Aug 2009
Posts: 1,635
Likes: 8
From: Enid Oklahoma
I won't even read anything from you from now on, so respond away if it makes you feel good, because I WILL NOT even look at it. Maybe it will make you more credible with those that do see it.
