Have You Tried A Quick Swap Of Pcms??

 

DTC P1518

Circuit Description

The throttle actuator control (TAC) module and the powertrain control module (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 test monitors the accuracy of the serial data transmitted between the TAC module and the PCM. If the PCM 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.
• The ignition voltage is more than 5.23 volts.

Conditions for Setting the DTC

• Invalid or missing serial data messages are detected for a predetermined amount of time.
• The above condition is met for more than 1 second.

Action Taken When the DTC Sets

• The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
• The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame and/or the Failure Records.
• The control module commands the TAC system to operate in the Reduced Engine Power mode.
• A message center or an indicator displays Reduced Engine Power.
• Under certain conditions the control module commands the engine OFF.

Conditions for Clearing the MIL/DTC

• The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
• A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
• A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
• Clear the MIL and the DTC with a scan tool.

Diagnostic Aids

Important: Reprogramming the PCM may cause a communication error between the PCM and the TAC. If the PCM detects a communication error, DTC P1518 sets. Clear any DTCs from the memory that may have been set by Reprogramming.

• DTC P1518 sets if the battery voltage is low. If the customer's 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.
• DTC P1518 sets when there is a short to B+ on the TAC module ground circuit. Inspect the fuses for the circuits that are in the TAC module harness--i.e. cruise, brake. An inspection of the fuses may lead you to the circuit that is shorted to the TAC module ground circuit.
• DTC P1518 sets if the TAC module ignition feed circuit is shorted to a B+ supply circuit. The TAC module stays powered-up when the ignition switch is turned OFF. When the ignition switch is turned ON, the TAC module is powered-up before the PCM. DTC P1518 sets because no communication is detected by the TAC module from the PCM. Inspect related circuits for being shorted to a B+ supply circuit.
• Inspect the TAC module power and ground circuits and the TAC module/PCM serial data circuits for intermittent connections.
• Inspect the TAC module connectors for signs of water intrusion. If water intrusion occurs, multiple DTCs may set without any circuit or component conditions found during diagnostic testing.
• When the TAC module detects a problem within the TAC system, more than 1 TAC system related DTC may set. This is due to the many redundant tests run continuously on this system. Locating and repairing an individual condition may correct more than 1 DTC. Remember this if you review the stored information in Capture Info.
• For an intermittent condition, refer to Intermittent Conditions

 

Hope That Helps..... Looks Like You May Wanna See If Your Ignition Switch Is Putting Full Voltage To It.... And Also Make Sure When You Moved The Tac You Didnt Short A Wire

 

Check to see if I have full voltage to what? Are you talking about the plug to the TB or the TAC? I have 2 different plugs on the TAC and the 1 on the TB. Can you point me in the right direction to which wires to check and I assume this is with the key in the run position? Thanks for the help it means alot.

 

Is it also common to get the service brake booster message along with the reduced power reading on the cluster?

I can not think for the life of me what could have happened to make this happen. I have no pedal input at all.

 

here man.... here is a link for a guy with a 2003 avalanche.... he had same problem including with brakes..

dtc problem

 

no roblem... i would hate to see you spend a bunch of money for someone to do something if you can

 

So I guess Im down to checking every wire in the engine bay, I will be back in about 2 weeks of searching for bad wires. How much TAC units?

 

no dont check every wire.... its more the ign positive on the tac box.... because if you read the link i gave you it says if the battery positive is shorted the tac will stay on constant even with the key off so it will throw a p1518 because it will not show the strtup communication, because the tac isnt supposed to power on until after the pcm..... check the connections at teh tac and tb first.... spray them out with compressed air, or use a spray can of electrical connection dryer.... use dielectric grease after you dry the wiring completely... and make sure there is no rust or corrosion at all on any of the pins... if there is try to use something to scrape or sand it down to bare metal

the communication to and from the tac box is very critical... if it shows improper data for only a second.... yes one second it will put you into reduced power mode.

ive also seen taht this code can happen if you torqued your tb too tight. it will cause the throttle blade to stick and throw the p1518 code

 

IGN positive on going into the TAC box. Now I just need to find out which color wire that is and take a good look at that wire. From what you are telling me there should be no power there? I will also look at how tight I put the TB down.