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hi everyone, i just bought my first corvette with a few issues that point me to a bad ecm harness
is a 98 corvette auto, when first bought it i replace the battery with a new yellow optima
got random engine codes, security, traction control and abs light on.
since i replace the battery only lights on left are security, abs and traction control lights
second thing i did was cleaning all the grounds except for the one on the rear near gas tank i didnt find it i also took apart the harness and nothing weird right
and also my fan 1 is not turning on, alredy check fuses and relays and its ok also if i put straight voltage to the the fuse box on the fan relay will turn on but not by them self
also i noticed today that my fuel gauge sometimes reads incorrect
any ideas where i can keep looking?? thanks!
Last edited by Alan Antillon; Mar 8, 2019 at 10:57 PM.
Reason: wrong title
you might want to pull up the codes and list them.
with the c5 being sensitive to low volts , a burned ignition switch will trip random codes.there are a few threads on how to replace/repair the ignition switch.i would check your switch to see what condition it's in. rockauto has new switches for a decent price.
Electrical issues atr commom on 97-98 C5's There was a problem with the column lock system-- You need to pull the codes and report back-- I would 1st try to have someone with a scanner delete al the codes and see if they come back--as mentioned often low voltages will trigger many codes--
Do you have schematics, you have to trace the fan switch back there are two circuits, a high (both fans) and low (a single fan). To me it sounds like you have a relay problem, see below, for the others does the battery gauge in the IPC show the charging voltage correctly and when you put a DVM across the battery do they agree and, if not you may have a high resistance in the ignition switch contacts causing the problem or the connections at the starter solenoid need cleaning.
if the service abs comes back at start up only and doesn't come on when driving there is a good chance it's the ignition switch
on my 2002 i would get the service abs/traction about every 12-15 start ups but it never came on while driving also had other codes pop up.changed my switch and all was good.
what happens is when you start the car all the systems want a certain voltage to respond. if the ignition has burned terminals those systems don't always get the voltage they want and trip a code.
...my fan 1 is not turning on, alredy check fuses and relays and its ok also if i put straight voltage to the the fuse box on the fan relay will turn on but not by them self...
Originally Posted by tentuna
...you have to trace the fan switch back there are two circuits... ...it sounds like you have a relay problem...
As mentioned above, there are 2 circuits:
Low Speed - with both fans connected in Series
High Speed - with both fans connected in Parallel
You have to troubleshoot both settings. Here are the schematics with the corresponding electrical paths superimposed.
Low Speed (Series Circuit):
High Speed (Parallel Circuit):
In a Series Circuit, any open point in the current path will prevent both fans from turning ON.
Since you mentioned that one of the fans is not turning ON, that means your Low Speed setting is not working at all and only when the High Speed kicks-in the "good" fan turns ON because the circuit changed to Parallel.
i have a snap on solus ultra, high speed fans work if i select to turn on in the scanner, but low speed is dead if set the trigger on and nothing but if i put 12v right where the relay goes it will turn on also check all 3 relays related to fans with a power probe and all 3 looks good ill take some pics once i get home with the codes aswell thanks for the replys!
well i just save the chase of wiring and i went straigh to c1 plug (blue) ecm connection on pin 42 as picture shown and i have no pulse or signal coming out from pcm so thats a bad pcm now right?
if it is ill be swapping the ecm but now if i have to get one ill be getting the 99+ but ill like to swap the harness aswell would a pcm and harness from a c5 99+ would fit on my 98 c5? i mean to save all the wiring swapping between c1 and c2 jand just doing a tune with a newer harness and pcm would that work ?well i just save the chase of wiring and i went straigh to c1 plug (blue) ecm connection on pin 42 as picture shown and i have no pulse or signal coming out from pcm so thats a bad pcm now right?
if it is ill be swapping the ecm but now if i have to get one ill be getting the 99+ but ill like to swap the harness aswell would a pcm and harness from a c5 99+ would fit on my 98 c5? i mean to save all the wiring swapping between c1 and c2 jand just doing a tune with a newer harness and pcm would that work ?
and about the swtich autozone ones works good?
thats how i make them work when i turn the car on all powertrain codes abs codes looks pretty durty for and ecm right thats 42 pin theres no signal at all
sorry i though fan1 was low speed but no both fans on low speed wont work just high speed
...sorry i though fan1 was low speed but no both fans on low speed wont work just high speed
In Low Speed, the coil from Relay 44 is not energized and C1 is connected to B11. Have you taken Relay 44 out and checked continuity between those 2 terminals on the relay? It should be 0 ohms.
If it tests fine, then it could be that the Low Speed trigger is not reaching Relay 45. It would be a good idea to check voltage across its coil (points G2 and E2 in schematic) to verify the presence of power when the Low Speed is supposed to kick-in.
well i just save the chase of wiring and i went straigh to c1 plug (blue) ecm connection on pin 42 as picture shown and i have no pulse or signal coming out from pcm so thats a bad pcm now right?...
You didn't mention how you were measuring the PCM's Low Speed Fan Trigger, or what you were expecting to read. Just to make sure we are on the same page, the trigger provided by the PCM on Pin 42 is ground and it is only present under very specific circumstances.
NORMAL fan operation on a C5 is as follows:
Low Speed - Triggered when coolant temperature reaches 226°F. When the coolant temperature drops to 219°F then the fans are turned OFF.
High Speed - Triggered if the coolant temperature rises to 235°F during low speed operation. When the coolant temperature drops to 226°F then the fans drop back to low speed.
With AC turned ON the cooling fans come on in low speed mode when the coolant temperature is about 185°F. The fans remain on in low speed mode until coolant temperature reaches 235°F, then they go into high speed mode.
If the vehicle speed exceeds 35MPH the PCM turns off the fans regardless of the coolant temperature. Air flow through the free-wheeling fans should be enough to keep temperatures within parameters, as long as the radiator fins are not plugged up. If they are plugged up, then the coolant temperature will rise and the fans will NOT come on unless the car goes below 35MPH.
You didn't mention how you were measuring the PCM's Low Speed Fan Trigger, or what you were expecting to read. Just to make sure we are on the same page, the trigger provided by the PCM on Pin 42 is ground and it is only present under very specific circumstances.
NORMAL fan operation on a C5 is as follows:
Low Speed - Triggered when coolant temperature reaches 226°F. When the coolant temperature drops to 219°F then the fans are turned OFF.
High Speed - Triggered if the coolant temperature rises to 235°F during low speed operation. When the coolant temperature drops to 226°F then the fans drop back to low speed.
With AC turned ON the cooling fans come on in low speed mode when the coolant temperature is about 185°F. The fans remain on in low speed mode until coolant temperature reaches 235°F, then they go into high speed mode.
If the vehicle speed exceeds 35MPH the PCM turns off the fans regardless of the coolant temperature. Air flow through the free-wheeling fans should be enough to keep temperatures within parameters, as long as the radiator fins are not plugged up. If they are plugged up, then the coolant temperature will rise and the fans will NOT come on unless the car goes below 35MPH.
like i said "i have a snap on solus ultra scanner" i can trigger almost everything electronic from the car with the scanner thats how i test it if i have signal to pin 42 and with a test light to check if i have signal but no is dead
Last edited by Alan Antillon; Mar 11, 2019 at 08:45 PM.
c5 electrical problems
As mentioned above, there are 2 circuits:
