98 vert 90k running fine until yesterday. Turning ignition key got some indication of car firing then nothing. Nothing in DIC to show codes. Check engine light lit dimly. After several attempts to start the starting motor would not activate.
Left it alone overnight. Today attempted to start. Turning ignition on got "Corvette" only as the start up message not the whole startup message then DIC went blank. Check engine light on, This time strong cranking for about 12 seconds but did not seem to fire at all like it did yesterday. Again unable to access any codes on the DIC readout.
Could be electrical, could be no fuel. The check engine light says the car knows something is wrong.
Any ideas on what is going on or how to diagnose and fix this problem?
Hey Big Hank !!...first thing I'd do is load test that battery...I do this anytime I perform diagnostics for any driveability issues. Next thing is checking for Tach movement during start...no movement equals no ignition or injector pulse (no cam crank signal)...if it is good next thing I check for spark...if spark good hook up fuel pressure gauge....my '01 is 55-62 psi static with pump running I and pressure drop is not more than shoot...can't remember the number, maybe someone who has the FSM in front of them can chime in...I'd start there...all you need is fuel, spark, and air to get her going !!...and yes, the CEL says something is wrong but she won't tell you !!...gotta run !!!...keep us advised !!
Sounds to me my no battery power to activate the electrical system. Several things to start checking. First is insure the battery connections are clean and tight INCLUDING the one at the starter solenoid. Next would be check the battery connection on the side of both the engine compartment fuse box and the passenger foot well fuse box to insure they are tight and clean. Next would be to pull the battery, have it fully charged and then load tested. Most parts stores will charge the battery and load test it free of charge.
This time of year the heat will kill a battery quickly easily especially if it is several years old.
Battery is only 3 months old but new does not mean good. Charged battery for over 24 hours with car electrical system disconnected. Reconnected terminals on battery. Voltage is about 12.5 with ignition turned off. Got partial DIC message "Corvette" then blank. Tried to read codes using Options and Fuel 4 times but nothing shows up. Tried to start car and got absolutely NOTHING. Connected jumper cables to another vehicle with engine running. Voltage read at Corvette battery with digital voltmeter now about 14.4 volts. Put key in ignition and turned it on but didn't turn to start. Got LOW VOLTAGE and REDUCED ENGINE POWER on DIC. Turned key to start and car cranked very fast but no start. Cranked for about 15 seconds and still no start. Tried this 2 more times. Now DIC says LOW VOLTAGE and 6.0 V battery. After several cranking attempts voltage dropped down to 5.6 V.
Either no spark or no fuel. Gas tank is full. Still cannot access normal functions from DIC and cannot access stored codes using OPTIONS and FUEL buttons.
What next? Bad ground? Computer malfunction? CHECK ENGINE LIGHT is on.
Battery is only 3 months old but new does not mean good. Charged battery for over 24 hours with car electrical system disconnected. Reconnected terminals on battery. Voltage is about 12.5 with ignition turned off. Got partial DIC message "Corvette" then blank. Tried to read codes using Options and Fuel 4 times but nothing shows up. Tried to start car and got absolutely NOTHING. Connected jumper cables to another vehicle with engine running. Voltage read at Corvette battery with digital voltmeter now about 14.4 volts. Put key in ignition and turned it on but didn't turn to start. Got LOW VOLTAGE and REDUCED ENGINE POWER on DIC. Turned key to start and car cranked very fast but no start. Cranked for about 15 seconds and still no start. Tried this 2 more times. Now DIC says LOW VOLTAGE and 6.0 V battery. After several cranking attempts voltage dropped down to 5.6 V.
Either no spark or no fuel. Gas tank is full. Still cannot access normal functions from DIC and cannot access stored codes using OPTIONS and FUEL buttons.
What next? Bad ground? Computer malfunction? CHECK ENGINE LIGHT is on.
Used an OBD code reader and got code P1518 - Power Control Module to throttle actuator control module serial data circuit code.
Using google found that this may be a bad connection in the wires going from these 2 modules or maybe a bad ground rather than the modules being defective.
Where are these modules?
Where are the serial data circuit wires and connectors?
What is the usual cause of this condition?
I have a similar problem. Went for about an hour drive today. Pulled into the driveway and turned off the car (no problems on the drive). Went to restart to roll the windows up and it won't even crank. Security light does not flash. It just starts cycling through the security messages on the bottom. Now I can't get the top out of the back (key fob, nor rear hatch switch are working) and the windows are down. HELP!!
Removed wheelwell cover and removed TAC which is bolted to the PCM. Used a DVM and service manual schematics and troubleshooting guide to check for continuity to plugs at TAC, Throttle Body Position sensor, Throttle Body Motor, and Accelerator Pedal potentiometers, and also the 2 wires going to the PCM (serial data lines). Had someone press accelerator pedal and saw resistances change on the lines to the TAC. Had battery tested and it showed good. It cranks engine at normal speed and does not seem to be week after 15 or 20 seconds of cranking, Looked at ground G106 near the starter. Used a long wobble shaft socket to slightly loosen the bolt and then tighten it to break loose any corrosion. This ground is almost inaccessible but I was able to tighten the large bolt. Have ordered a replacement TAC which should arrive tomorrow. Will see shat happens when I replace the original TAC. Anyone who has been thru this situation is welcome to comment on addition actions to solve this problem.
I basically had the same issue 2 weeks ago you have...had P1518...low voltage on DIC ( 5-6 volts)...PCM NO COMM...with scan tool hooked up no TAC voltage response pushing accelerator pedal down...was also a no crank no start...no fuel pump prime when key turned on...I know my battery is fine because I load tested early last month and did a starting system check with my scope and all related grounds were cleaned this summer...after seeing the low voltage on the DIC I cycled the ignition switch quickly a bunch of times and it started and then I could not duplicate the problem again...changed the ignition switch !!...BTW did you check your serial data line with a DVOM ??...you’ll see some voltage but not the correct 0-7 volt square wave using a scope..,a DVOM can not process the serial line data voltage quick enough and Your P1518 code was thrown because of that low voltage the PCM was seeing at the TAC module !!
Have another ignition switch, will change if new TAC doesn't fix the no start
Quote:
Originally Posted by rwobs777
I basically had the same issue 2 weeks ago you have...had P1518...low voltage on DIC ( 5-6 volts)...PCM NO COMM...with scan tool hooked up no TAC voltage response pushing accelerator pedal down...was also a no crank no start...no fuel pump prime when key turned on...I know my battery is fine because I load tested early last month and did a starting system check with my scope and all related grounds were cleaned this summer...after seeing the low voltage on the DIC I cycled the ignition switch quickly a bunch of times and it started and then I could not duplicate the problem again...changed the ignition switch !!...BTW did you check your serial data line with a DVOM ??...you’ll see some voltage but not the correct 0-7 volt square wave using a scope..,a DVOM can not process the serial line data voltage quick enough and Your P1518 code was thrown because of that low voltage the PCM was seeing at the TAC module !!
I replaced ignition switch a couple years ago because the front part which touches the resistive pellet on the key was not working. I could remove the 2 plugs (white and black) which are in the back of the switch and see if the old switch starts the car. Will be a PITA to get to the switch as you have to remove the plastic in front of it to get to the plugs.
How did you get scope probes on the serial data line which goes from the TAC to the PCM? I did my measuring with the plugs removed and not able to get the readings when trying to start the car. I have a decent scope but am hesitant to puncture the wires from the TAC to the PCM as thats where moisture can get in and corrode or short out the wiring. I had the PCM replaced about 2 weeks after I bought the car as the battery acid got in and ruined it. that was about 17 years ago.
There are a lot of threads here about random/bizarre electrical issues caused by bad grounds. I went through something like that with my own car just a week or two back.
Fortunately there are also a lot of threads about where the grounds are and how to inspect them. Start with the ones under the hood, on frame rails behind the headlights. They seem to be very susceptible to corrosion.
I replaced ignition switch a couple years ago because the front part which touches the resistive pellet on the key was not working. I could remove the 2 plugs (white and black) which are in the back of the switch and see if the old switch starts the car. Will be a PITA to get to the switch as you have to remove the plastic in front of it to get to the plugs.
How did you get scope probes on the serial data line which goes from the TAC to the PCM? I did my measuring with the plugs removed and not able to get the readings when trying to start the car. I have a decent scope but am hesitant to puncture the wires from the TAC to the PCM as thats where moisture can get in and corrode or short out the wiring. I had the PCM replaced about 2 weeks after I bought the car as the battery acid got in and ruined it. that was about 17 years ago.
Oh, OK...you changed the switch. ..you talking about the orange/black and tan wires from the TAC to the PCM ??...when you say you removed the "plugs" I'm thinking you are talking about the shorting bar on the class 2 line at the BCM area ??... now if this is what you'd want to do there is NO problem puncturing the wire...I use liquid electrical tape to cover the small puncture...done it many times...forget about removing the 2 plugs from the ignition switch...you'll have to remove the center console, IP trim plate and knee bolster...I actually finished my switch replacement this morning because I was waiting for a new switch bezel that was broken when I removed it...you really need a scan tool to see if you can communicate with ALL the modules...a code reader won't cut it...if you are thinking it's the ignition switch when you are getting the low voltage on the DIC you can check the crank fuse (#14 to see if you are getting system voltage through the ignition switch to that fuse...and as far as G106 you really have to get under there and physically clean the terminal ends !!...if you want I can show you how to check the class 2 serial data lines with a quick video if that is what you are trying to accomplish...I enclosed a picture of my class 2 serial data line waveform from my scope...0-7 volts !!
Got a different used TAC which came out of a 2002 C5, (mine is a 1998). Has a different PN but the cross reference list on several sites on the internet say that they are all interchangable.
Next item is remove Ignition Switch (2 plugs - white and black) and try starting with the other switch. It was removed from my car several years ago because the 2 contacts in the front of the locking mechanism which read the keys resistor pellet were shot. The current switch has worked fine for several years. When I tried to turn the lock mechanism on the former ignition switch I replaced several years ago with the original key it wouldn't budge. I finally drilled out part of the center of just the locking mechanism and can use a flat blade screwdriver to go to the the various positions from LOCK ACC ON and START.
On the OLD switch, I CAN"T GET the LOCK CYLINDER OUT OF THE ELECTRICAL OR REAR PART OF THE SWITCH. Have posted that as a separate thread. I have tried to go to the ON position and use a small screwdriver to depress something on the cylinder where a slotted line appears at that position, but so far have not be able to remove the cylinder. IF the old ignition switch starts the car I wold like to remove the broken cylinder and put the newer working cylinder (in the ignition switch now on the car). Any ideas here on removing the broken cylinder from the alternative ignition switch would be appreciated.
Thanks for the picture. I found the same picture in my 1998 Corvette Service manuals but did not know it was there until i did a diligent search. I was pressing a screwdriver on the other rectangular hole 180 degrees from the smaller hole in the picture. Did successfully remove the lock cylinder. Now all I have to do is rip the car apart to get to the Ignition Switch.
Dissected the dash to get to the Ignition Switch. Found a NOS back part of a C5 switch (D1499C) and also have the original switch I replaced several years ago which had defective sensors in the front at the lock cylinder to read the resistance in the VATS pellet.in the Ignition Key. Decided to go with the new switch first and see if the car would start. Used an OBD reader to read and reset the P1518 code which comes on immediately when turning on the ignition. Turned on the ignition and read and erased the P1518 code. Turned the key to start...engine cranked and THIS TIME STARTED. It WAS the Ignition Switch not the TAC, throttle body, or TB position sensor, or potentiometers in the throttle pedal. P1518 code was misleading. Caused me to acquire another TAC module. Was getting dark so I closed up the car and will do some more work on it tomorrow.
Something strange... With car running could not access codes from the DIC. Will look at that again tomorrow.
Thanks for the ideas. That's what this forum is about.
UPDATE: Now I can read codes from the DIC. Maybe the DIC was tired and just needed a rest. Thats what they told me in the Bahamas when the glass bottom boat which I had paid for wouldn't go out to sea.
