just won't start and it has no spark

[jeffyp32]

about a month ago my car was running fine then i parked it and came back 5 min later and it would idle fine but would have enough power to move so i parked it for the rest of the night and came back to it and it ran fine. parked it the next day and now it wont start. it says reduced engine power and the code is "pcm to tac". i tried a new throttle, new battery, new coils, new wires but nothing is working i tried to see if the spark plugs were getting spark but nothing. anything right now would help so i dont have to take it to a mechanic and have him rape my banking account!!!!

[Blizzard242]

Re: just won't start and it has no spark

What code specifically is it?

[jeffyp32]

Re: just won't start and it has no spark

i think its p1518-pcm to tac module serial data circuit

[Blizzard242]

Re: just won't start and it has no spark

I'm kind of curious why you changed all of those things when your car was throwing a code of that nature...?

[Blizzard242]

Re: just won't start and it has no spark

From the LS1Tech forums.

DTC P1518 Throttle Actuator Control (TAC) Module Serial Data Circuit

Circuit Description
The TAC module and the PCM communicate via a dedicated serial data circuit. This serial data circuit is separate from any other serial data circuit on the vehicle. Accurate transmitting and receiving of serial data requires not only good circuit integrity but also adequate system voltage. This diagnostic monitors the accuracy of the serial data transmitted between the TAC module and the PCM. If the PCM/TAC module detects a loss of data or invalid data, this DTC sets.

Conditions for Running the DTC
The ignition switch is in the crank or run position.

Conditions for Setting the DTC
Invalid or missing serial data messages are detected for a predetermined amount of time.

Action Taken When the DTC Sets
The PCM will illuminate the malfunction indicator lamp (MIL) during the first trip in which the diagnostic runs and fails.
If equipped with traction control, the PCM will command the EBTCM via the serial data circuit to turn OFF traction control and illuminate the TRACTION OFF lamp.
The PCM will store conditions which were present when the DTC set as Freeze Frame/Failure Records data.
Conditions for Clearing the MIL/DTC
The PCM will turn OFF the malfunction indicator lamp (MIL) during the third consecutive trip in which the diagnostic has run and passed.
The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
The DTC can be cleared by using a scan tool.
Diagnostic Aids
Inspect for the following:


Important
DTC P1518 sets if the battery voltage is low or the PCM is replaced/reflashed. If the customers concern is slow cranking or no crank because battery voltage is low, ignore DTC P1518. Clear any DTCs from memory that may have set from the low battery voltage condition.


The following could cause an intermittent condition:

Many situations may lead to an intermittent condition. Perform each inspection or test as directed.

Important: : Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.


• Loose terminal connection

- Use a corresponding mating terminal to test for proper tension. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair.

- Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair.

• Damaged harness--Inspect the wiring harness for damage. If the harness inspection does not reveal a problem, observe the display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the scan tool display may indicate the location of the fault. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair.

• Inspect the powertrain control module (PCM) and the engine grounds for clean and secure connections. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair.

If the condition is determined to be intermittent, reviewing the Snapshot or Freeze Frame/Failure Records may be useful in determining when the DTC or condition was identified.

Test Description
The numbers below refer to the step numbers on the diagnostic table.

When the PCM detects a problem within the ETC System other DTCs may set due to the many redundant tests run continuously on this system. Locating and repairing one individual problem may correct more than one DTC. Keep this in mind when reviewing captured DTC info.

[jeffyp32]

Re: just won't start and it has no spark

i asked this question before and the only reply i got was to charge the battery so i just bought a new one but it didn't work so i just returned as with the coil and throttle body. so now i'm out of ideas.

[Blizzard242]

Re: just won't start and it has no spark

Check your PCM harness for ANYTHING that looks less than perfect. Look at your ground wires. You should have 2, one from the block to fusebox assembly area and another around the AC compressor. Of course check the integrity of your positive battery cables. uhmmm All of your fuses.

I dunno, I have a feeling something is wrong with your PCM or harness itself.

[jeffyp32]

Re: just won't start and it has no spark

thats kinda what i was thinking

[jeffyp32]

Re: just won't start and it has no spark

does anyone know where i can find a new pcm

[chevy3504me]

Re: just won't start and it has no spark

craigslist look for a part car. I didnt read this entire post but you can find one or craigslist. I think i can get them for $100. If you want one PM me, I can check to see if I can get one.

[jeffyp32]

Re: just won't start and it has no spark

thanks for the help. i'm gonna look at it tomorrow and see if the pcm is even getting power. i'll let everyone know how it goes

[flamingchicken]

Re: just won't start and it has no spark

pcmforless.com will sell you a tuned pcm for pretty cheap.

[jeffyp32]

Re: just won't start and it has no spark

well i got it started. not the pcm what so ever. it was the ign fuse (the silver sqaure fuse) i didnt even think of it but i touched it and it was on fire. so it started but blew out the throttle gasket and sprayed coolant everywhere (especially into the actuator) so that throttle is f**ked. but i ordered a new gasket and i have a spare throttle luckily

[Blizzard242]

Re: just won't start and it has no spark

well i got it started. not the pcm what so ever. it was the ign fuse (the silver sqaure fuse) i didnt even think of it but i touched it and it was on fire. so it started but blew out the throttle gasket and sprayed coolant everywhere (especially into the actuator) so that throttle is f**ked. but i ordered a new gasket and i have a spare throttle luckily

At least you figured out what the problem was.

[jeffyp32]

Re: just won't start and it has no spark

yeah but when i started it i ran another scan to see if the code was there. it wasnt but then it came back so im not sure whats up with that and i got two different fuel injector codes, something else with the TAC and another one that i forget but it was something that said it was vs something