Hard starting, code 15, help needed
Thread Starter
Instructor
Joined: May 2011
Posts: 103
Likes: 2
Hard starting, code 15, help needed
I recently installed headers, removed A.I.R. system and everything was running fine until it threw a code. I jumpered the pins and got code 15, which is low coolant temp. Since I installed a 160 degree thermostat a few months ago I thought maybe it was running too cool between 154 and 160 on a cool morning. I put the stock 180 thermostat back in.
The main cooling fan continues to run constantly and it runs a little rough until it warms up, and then it runs fine. I replaced the main cooling fan relay, temp sensor, cooling fan sensor , I have d/c the battery to reset the ecm and still have the issues. The temp gauge reads LO until it gets to 100 and then it seems to run better, I don't know. Please help
1987 L98 with BP4 option, thermo coated headers, new bosch III injectors, new EGR, 180 degree thermostat.
Can the car be driven with the main cooling fan constantly running without any problems? Once in a while the SES light will go off for about 2 or 3 minutes and come back on while driving. All A.C connections are connected.
Thanks
The main cooling fan continues to run constantly and it runs a little rough until it warms up, and then it runs fine. I replaced the main cooling fan relay, temp sensor, cooling fan sensor , I have d/c the battery to reset the ecm and still have the issues. The temp gauge reads LO until it gets to 100 and then it seems to run better, I don't know. Please help
1987 L98 with BP4 option, thermo coated headers, new bosch III injectors, new EGR, 180 degree thermostat.
Can the car be driven with the main cooling fan constantly running without any problems? Once in a while the SES light will go off for about 2 or 3 minutes and come back on while driving. All A.C connections are connected.
Thanks
Instructor
Joined: Jun 2011
Posts: 182
Likes: 0
From: Bowling Green Ky
I recently installed headers, removed A.I.R. system and everything was running fine until it threw a code. I jumpered the pins and got code 15, which is low coolant temp. Since I installed a 160 degree thermostat a few months ago I thought maybe it was running too cool between 154 and 160 on a cool morning. I put the stock 180 thermostat back in.
The main cooling fan continues to run constantly and it runs a little rough until it warms up, and then it runs fine. I replaced the main cooling fan relay, temp sensor, cooling fan sensor , I have d/c the battery to reset the ecm and still have the issues. The temp gauge reads LO until it gets to 100 and then it seems to run better, I don't know. Please help
1987 L98 with BP4 option, thermo coated headers, new bosch III injectors, new EGR, 180 degree thermostat.
Can the car be driven with the main cooling fan constantly running without any problems? Once in a while the SES light will go off for about 2 or 3 minutes and come back on while driving. All A.C connections are connected.
Thanks
The main cooling fan continues to run constantly and it runs a little rough until it warms up, and then it runs fine. I replaced the main cooling fan relay, temp sensor, cooling fan sensor , I have d/c the battery to reset the ecm and still have the issues. The temp gauge reads LO until it gets to 100 and then it seems to run better, I don't know. Please help
1987 L98 with BP4 option, thermo coated headers, new bosch III injectors, new EGR, 180 degree thermostat.
Can the car be driven with the main cooling fan constantly running without any problems? Once in a while the SES light will go off for about 2 or 3 minutes and come back on while driving. All A.C connections are connected.
Thanks
if it is low reading, but normal ambient, the fuel will be too rich.
not sure what the fan problems are. may not be related.
Thread Starter
Instructor
Joined: May 2011
Posts: 103
Likes: 2
you replaced the coolant temp sensor that sends signals to the ecm? did I read it right? on the 90 it is below TB, a yellow and a blk wire, if it reads low or high the ecm changes fuel to injectors accordingly. code 15 is reading that signal, not the actual temp of coolant, the way I understand it.
if it is low reading, but normal ambient, the fuel will be too rich.
not sure what the fan problems are. may not be related.
if it is low reading, but normal ambient, the fuel will be too rich.
not sure what the fan problems are. may not be related.
Instructor
Joined: Jun 2011
Posts: 182
Likes: 0
From: Bowling Green Ky
I speak from my 90 experience, but the ecm controls fans, from inputs from CTS, a/c, and vehicle speed sensor. yours has the fan switch in the head, I reckon. have read many forums where it was the problem with over rich condition, but gages read fine.
Instructor
Joined: Jun 2011
Posts: 182
Likes: 0
From: Bowling Green Ky
Thread Starter
Instructor
Joined: May 2011
Posts: 103
Likes: 2
At least I shouldn't have to replace any temp, fan sensors or senders for a while
Burning Brakes
Joined: Nov 2008
Posts: 995
Likes: 1
From: Naples Campania
It's surprising how much havoc that sensor can cause.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
2027 Corvette vs The World: Every Model vs Closest Competitor
Joe Kucinski
10 Most Common Corvette Problems of the Last 20 Years!
Joe Kucinski
5 MOST and 5 LEAST Popular Corvette Model Years in History!
Joe Kucinski
2027 Corvette Buyer's Guide: Everything You Need to Know!
Joe Kucinski
10 Things C8 Corvette Owners Hate (But Won't Tell You)
Joe Kucinski
10 Best Corvettes Coming to Barrett-Jackson Palm Beach 2026!
Brett Foote
Every Corvette Grand Sport Explained! (C2, C4, C6, C7, & C8)
Joe Kucinski
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
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
FYI: Sensor is used for fuel delivery. A thermistor, it's resistance decreases as it warms up. That causes the 5 volt reference from the ECM to drop and that voltage drop is used to calculate coolant temp. A 15 means there's no drop - circuit is open and if you had a Scanner it would show an impossible coolant temp of -38 degrees. That's allmost always a wiring issue and not the Sensor, though if you've broken or snapped the Sensor in two doing repairs, that could certainly cause the Code. The opposite, a Code 14, occurs when the Reference wire is grounded and the ECM sees 0 volts. A scanner would show a Coolant temp of 300 degrees. This too is usually a wiring issue. Most problems with the Sensor - other than breakage - occur when the internal resistance weakens and it can no longer send an accurate coolant temp to the ECM. That mucks up fuel delivery and causes driveability issues for which there are no Codes.
Instructor
Joined: Jun 2011
Posts: 182
Likes: 0
From: Bowling Green Ky
FYI: Sensor is used for fuel delivery. A thermistor, it's resistance decreases as it warms up. That causes the 5 volt reference from the ECM to drop and that voltage drop is used to calculate coolant temp. A 15 means there's no drop - circuit is open and if you had a Scanner it would show an impossible coolant temp of -38 degrees. That's allmost always a wiring issue and not the Sensor, though if you've broken or snapped the Sensor in two doing repairs, that could certainly cause the Code. The opposite, a Code 14, occurs when the Reference wire is grounded and the ECM sees 0 volts. A scanner would show a Coolant temp of 300 degrees. This too is usually a wiring issue. Most problems with the Sensor - other than breakage - occur when the internal resistance weakens and it can no longer send an accurate coolant temp to the ECM. That mucks up fuel delivery and causes driveability issues for which there are no Codes.
good inputs, thanks.
