SUPERCRUZ

Need advice from you seasoned tech gurus. Weather was nice today so I decided to start the Vette up and let it idle in the driveway while I touched up my wheels. Car has been sitting on a battery tender for about 6 weeks now due to poor weather and road conditions in NOVA. Car ran fine with no issues when I parked it in early December. When I went to turn the key, I decided to cycle the key two times for some reason to give it an extra shot of fuel at startup and up pops messages, Reduce Engine Power, Service TCS. I examined codes and found PCM P0606 and P1518 as well as TCS C1276. I tried several more attempts at recycling the key and by resetting codes but codes will not re-set. I also disconnected the battery for well over 10 min and reconnected. Same condition. Tried to start. Engine cranks stong but does not fire.

My research indicates the car is in a total shut down mode. Appears the TAC is not receiving the necessary communication for low voltage from the PCM. I have checked the #17 Throttle Control circult and it is OK. My next step is to pull the right front wheel and remove the access panel to the PCM and TAC modules. I will also check grounds and wires in that area. Am I on the right track here? Car is not driven in rain but does sit in a car port under a cover so it is somewhat open to the elements. Any other advice on dealing with this situation is appreciated.

Man I love my Vette but this really has me bummed out. Rain expected tomorrow so I was looking forward to pulling this thing out of hybernation for a run on Monday after all the salt is washed off the roads. Guess that is out the window for now. Appreciate some guidance here.

lucky131969

Check the condition of fuse #17 in the under hood fuse box. If it's ok, check for 12 volts on the line side with the key on.

SUPERCRUZ

I am wondering now if my battery took a dump. It is always maintained on a battery tender but now that I put it back on the tender for the past hour, it does not appear to be coming back up. Light is still red. This is an Optima Red Top that is about 5 years old. No complaints. It has served me well. Boy will I luck out if that is all this turns out to be. I should know for sure in a few more hours if the battery does not come back to full charge. Do you guys thiink a failing battery could result in the P1518 and P0606 codes and Reduced Engine Power. Car seemed to crank fine but I did not crank it for more than a few seconds and only did it twice. Can I test the battery with a Volt Ohm meter and what am I looking for, 12 volts at the terminals?

lucky131969

Yes, a low battery can precipitate a P1518 for sure. You can check the battery with a volt meter, but you may just read a surface charge. The only way to evaluate a battery is with a load test. Provided you do not have a shorted cell, if the battery is the issue, you should be able to jump start the car.

SUPERCRUZ

Well, my battery tender is showing fully charged right now. The car did crank very easily when I tried to start it earlier today so I am guessing the issue is not the battery. I am leaning back toward thinking the problem might involve the TAC module. I will have to check that on Monday. I may pull the battery and have a load test performed just to rule that out. Others with ideas or experiences dealing with a similar issue are welcome to comment.

lucky131969

I already posted my first suggestion to start troubleshooting, post #2. Can you hear the fuel pump prime?

In any case, I'm sure Bill will be checking in soon..........

SUPERCRUZ

Already checked Fuse #17 and it was good. I will try and listen for the fuel pump priming. Thanks for all your advice. Hope Bill C checks in. I would be interested in hearing his take on things. Just finished reading all his posts on checking grounds. Thanks again.

John

lucky131969

So you checked for 12 volts to fuse #17?

SebringSixSpeed

I had the same symptoms awhile back. I went through tons of troubleshooting. Turned out to be poor conductivity at the internal ignition switch contacts. I hope for your sake its not the TAC module because they are currently on national backorder. You can see my post here

lucky131969

Yep. That's why I was asking him to check 12 volts to fuse 17. It supplies 12 volts to the TAC, and is in turn powered by ignition relay 42, which is thrown by the ignition switch..

SUPERCRUZ

Guys - Okay, so I ony checked the condition of the #17 fuse. How do I check for 12v at #17? Do I pull the fuse and probe the left and right side of the fuse slot with my volt meter with the ignition in the ON postion? Thanks for clarifying this for me.

lucky131969

Yes. One side should be battery voltage, and one side should be zero. Can you hear the fuel pump prime when you turn the ignition on?

SebringSixSpeed

There should be two small holes in the top of the fuse. If the fuse is not blown it does not matter which side you probe for 12V. Obviously the pictures don't show the fuse installed, but you get the idea and the other lead from the multimeter will be grounded.

SUPERCRUZ

SebringSixSpeed. Dumb question but where is the fuel pump fuse located? I was looking at the main fuse block under the hood at the number 17 fuse. This appears to be a mini fuse, 15A as I recall. I do not remember these probe points on these mini fuses.

Lucky131969 - I do need to check to see if the fuel pump is running. Hard to hear with all the DIC chimes and bells going off. As soon as the weather breaks, I will see if I can position myself to hear the fuel pump priming with someone else turning the key to the ON position.

Thanks guys. I will update you when I know more.

SebringSixSpeed

No such thing as dumb questions. My mini fuses have the test ports. The following info is based on my knowledge of my 1998 C5, so that being said there may be a difference on the layout of your 2003, be sure to verify for yourself please.

Fuse #13 is the fuel pump fuse as illustrated and the relay next to it is the one you want to jumper



I use a jumper made with fuse blades soldered to the jump wires. I also use an interupt switch and a fuse holder. I have used this for testing several things on my car and it has been very handy.



Now this is the way to jump the relay (on a 98) with this in position and the ignition switch in the run or start position the fuel pump will run if the fuel pump and the wiring from the underhood relay center to the pump is good. This will bypass the PCM but not the voltage from the ignition switch



Heres the logic, and you are jumping from point 30 to point 87.

SUPERCRUZ

SebringSixSpeed - Thanks. Here is the latest. Other posts I read said check fuse #17 which is the ThrottleCtrl fuse. Pulled that fuse and tested circuit with Volt meter. Getting 12.25 volts. I then checked fuse #13 which looks fine and tested with Volt meter and got a steady 12 volts with the ignition in the ON postion. Seems like Ignition switch cause would be unlikely.

For the life of me I cannot seem to hear the fuel pump priming or running each time I cycle the key. I have cycled the key at least a dozen times and no fuel pump sound. I checked the fuel pressure at the drivers fuel rail with ignition in ON postion by simply pushing the schraeder valve with my finger and a rag. Fuel pressure seems low to non existant to me. I would have expected fuel to really spray out of there with some force if it was under 65 psi or higher.

I pulled the #35 FPump Relay and swapped it for the same relay type #36 Horn Relay. Nothing. Same issues.

What else would cause the fuel pump to not run and prime? I guess my fuel pump could go bad but seems unlikely. Is the PCM shutting fuel down due to the NO Run condition with codes P0606 and P1518 together? Will jumping the relay the way you show in your pics above run the fuel pump regardless of the PCM? I plan to look at the TAC wiring and G104 ground near the starter on Monday. I may also check the grounds at the rear of the vehicle as well. Thanks again.

John

SebringSixSpeed

Yes, jumping as shown will totally bypass the "fuel enable" signal from the PCM. This will help you to isolate the problem. If you jump the fuel relay and the pump works that will tell you that your pump and related wiring is good, but that is basically all it tells you. As far as I know a bad fuel pump will not set P1518 so I doubt that's your problem.

I would not rule out the ignition switch just yet. It's pretty easy to remove and polish the contacts. I'm sure you've seen Bill Curlee's "how-to" in the sticky section.

There are no less than 5 contacts inside the switch that send 12V to various places including the PCM and TAC module. There is a chance that the contact sending 12V to the fuel pump fuse is ok but the contact sending 12V to the TAC module is not ok. If there is any low voltage condition or other fault within the TAC system (that includes the ignition switch, the TB, the pedal, and the TAC module itself and all related wiring) the PCM will cut power to the fp relay and the injectors and set DTC P1518. So even if you jumper the pump to come on, the injectors will not respond and the engine will not run. This is the root cause of P1518 and is basically a safety feature in the "drive by wire" concept to ensure the vehicle does not go WOT if there is a fault.

The TAC modules are pretty robust and not prone to failure (with the exception of some early 98's) and I doubt it is your problem as they were updated several times prior to 2003.

lucky131969

Ok. I'll make some final comments here. I'll PM you my number if you have questions.

If you do not hear the fuel pump prime when you turn on the ignition, this should be your focus. The fact that you have 12 volts to the line side of fuse #13, tells you that you are getting 12 volts from the ignition switch, and this voltage is provided to the fuel pump relay contact(provided the fuse is good).

As already discussed, you can jumper the relay socket, and the pump should run continuously with the key in "on". If it runs, you know 12 volts is good from the ignition switch to the pump(already cited).
If it does not run, you are down to pump/wiring. Should you get the fuel pump to run with the jumper, try starting the car....it should fire...

If it runs, you now have to determine if the PCM is providing 12 volts to the fuel pump relay, and also make sure the relay has a good ground. The fuel pump relay gets a ground from SP122, which in turn, it grounded at G105(lower left side of the block).

lucky131969

I'm not sure what service manual this is from, but the ground location for the fuel pump relay is not correct.

SebringSixSpeed

The schematic is from my factory GM 1998 Corvette Service Manual Vol 3 of 3. Like I said, OP's car is 2003, mine is 98, just trying to help out with some ideas he could translate to his year model.