Reduced Engine Power Message/ Service Engine Soon

Reduced Engine Power message and service engine soon came on last week. Code reader put out P1518 and P1518/freeze frame. I checked continuity on all El/gas petal wires (ok). I have not replaced throttle body or gas petal yet... Owners manual says if you have 8.1 engine it might involve them.                                I also  opened up the wire harness to look for bad wires.... and found some. All the way back against the firewall where the heater hoses go thru, the wires were rubbing on the hose clamp. All the way thru a black ground wire and part way thru a gray wire. (they were touching) The gray one is paired with a yellow wire. They go to a sending unit on the passenger side head, above the #6 spark plug. The s-unit has 2 black & a green wire. I need to know what is that sending unit, did it get fryed? How do I test it? And could this be the root cause of the Reduced Engine Power message?    More... I tryed to erase the code but it keeps popping back    Are their any diagrams of where 8.1 sensors are? I did search and found what "Sperry" posted about those codes.    I'm gratefull for any help.    Also I've been around for a couple a years now, but this is my first thread!    Dave

Apparently you have a later 02 (unless all 8.1's in 02 have the electronic throttle).

TAC and TPS work together for safety purposes. One runs off the TAC motor to sense the position of the throttle motor as commanded and the TPS monitors it. If they don't agree, you get the message.

Better to have "reduced engine power" than full uncontrollable throttle!
Simply put, one failed! The code says the TAC module did. That can also be the connector, so before you shell out the bucks, keep checking. And particularly that module and wiring, as you checked something of the sort already.

If I remember, GM doesn't sell that part in pieces. That may be just the 5.3. Instead, it's the whole thing only. (Double check that! I just read it somewhere in the past!) Check with an aftermarket parts supplier. It may be just the sensor or some replacable part rather than the whole $$ thing.

And, I suggest you wait for a few more responses, especially from someone who experienced it themselves.

Good luck!

The TAC module is HERE, but it's not the motor/sensor. The codes depict IT as the bad part. Could even be a fuse! (ETC fuse, 15A near the center of the underhood fuse box.) Then, what blew it? Your bare wires?

I didn't get all the 2500 info when I had a chance. Other members just may have the motor/sensor part breakdown. All I had was the 1500.

Again, good luck!

I used to get this once every 6 or 8 months. Now I get it at least once every few days. I remove and replace connector to the throttle body and then I am fine for a few more days. It never happens while I drive--only on start up

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 is turned OFF. When the ignition 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. When this occurs, multiple DTCs could be set with no circuit or component conditions found during diagnostic testing.

When the TAC module detects a problem within the TAC system, more than one TAC system related DTC may set. This is 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.

Here's a link to the TSB for the 8.1

Hope this all helps..

Hmmm, that covers the 03's... Oh well.

-------------

I'm wondering if this is another spin-off quirk of the resistive/intermittent ign switch?

If low batt voltage will set the DTC and the message, perhaps that could too. I would need to see where the TAC module's power source is.. Batt + or Ign switched.

Howdy! Thanks for the replys & the HUGE amount of information. I'll be reading for a while! lol  I could'nt wait, I ordered a TAC from the dealer. ($194.61) Oh well.  Sperry, I replaced the Ign switch just over a year ago. Maybe I got another bad one?  Before I go further....    I should mention the night before this happened we had a lightning storm. I saw a huge flash and I presume their was a boom too.   (I've been deaf for a long time)   A breaker in the house was tripped, this computer screen color changed and another computer in the other end of the house went wonkey. The Avalanche was parked out front. The truck starts, I can move it, but it's stuck in reduced engine power mode. Would'nt the truck be totally dead if hit by lightning? Opinions please    A long day in Pittsfield Mass. today... Gotta go get something to eat. Back soon.

After doing some reading on the links, I'm removeing my K&N drop-in air filter. I'll try the new TAC this afternoon.

Hey there everyone.  New TAC not here yet    Next I'm going to check power wires to TAC and plugs under electrical center. When I did the fulltime drl"s you flip over the fuses to get at the double blue wires. Maybe one loosened up when I did that.    After that I gotta go pay some bills. I'm driving my brothers POS  Furd ranger while all this is going on.  How embarassing! But at least it works.....

      I have an update.. and the news is good! Installed the new TAC module, the plugs felt more snug and firm. Started the truck, the reduced power mesage was gone. Service engine soon light went out when erased with that Walmart code reader I got awhile back. Because the part was delayed a couple a days, the parts guy gave an extra $25 bucks off.    It was "plug & play".... no extra screwing around reflashing or whatever.          A  BIG "THANK YOU " go out to sperry, ItsStopher & cadboy1 for your help in solving the dredded "reduced engine power " problem!     

            Now I can drive to the paint shop where a new ramair hood is waiting!