Ok so couple days ago my car started acting weird, idling really bad and loosing power I barley made it home when it completely shut off. I turned the car on again but now the idling was even worse car shaked and I got the “reduce engine power” checked the codes and I got P1120, p1220, and p1516 and car won’t go past 2k rpms even when you step on the gas. I replaced the throttle body with my friend’s c5 throttle body but the car is still doing the same thing, i did a little bit of research and I found out I might need to replace the TAC module now. Anything else I should check before replacing the TAC module?

 

Moved to C5 Tech.

 

P 1120 and P1220 is for the "throttle position sensor and not the TAC control
With some sort of scanner or data logger see if you throttle position sensor is working correctly
P1514 thru P1516 may indicate a faulty TAC But I would 1st fix the throttle position sensor issues as when repaired may fix the TAC code as well
ALSO Only on highly modded engines you will need to alter the "predicted airflow table" which triggers a P1514 to P1516 code
A stock engine should not need an adjustment however when your mods exceed about 70 HP your ECM will exceed the predicted airflow and the car will go into reduced power mode The fix is to add like 25% to that table In EFILIVE it is table C6101

ALSO are you getting any "wheel sensor codes" These will also trigger a TAC code as the traction control system uses the T Body to reduce TQ via the TAC

 

If you changed the TPS sensor I’d concentrate on the wiring...TPS, APP and also the TAC module !!...TPS is basically 2 potentiometers in one housing..,each being 3 wires...a 5 volt reference, a sensor ground, and a signal wire...I would start checking that...with key ON backprobing the connector you should have less 100mv on the sensor ground, and 5 volts on the reference...TPS 1 the voltage goes from low to high as the gas pedal is depressed and the other TPS 2 voltage goes from high to low...a scope is best to do what they call a TPS Sweep !!...looking for any drop outs in the voltage...if the PCM sees a voltage difference that’s excessive the DTC will set !!...a multimeters refresh rate is not high enough to capture these dropouts !!...I've enclosed a TPS Sweep video on my 2001 !!

 

I did replace the tps but it did nothing still kept getting the same codes, I’ll be looking in to the wiring next checking all the grounds and connections

 

I forgot to mention I did replaced the tps but car was still acting the same, I was also getting code c1278 “TCS temporally disabled by PCM” my car is completely stock other than exhaust cutouts

 

I would first take your multimeter and check all 6 TPS wires...2 will be have 5 volt (dark green and yellow/black)... 2 are signal (dark blue and pink), and 2 are sensor grounds (grounded at the PCM) the white and purple)...as I had said with key ON less than .1 volt on sensor ground...if you can get some back probes or t pins great. What year and mods are in the car ??....please put that in your profile...this helps us help you. The 1120 sets if TPS 1 signal voltage is less than .13 volts or more than 4.87 for LESS than 1 second....P1220 sets if TPS 2 signal voltage is less than .13 volts or MORE than 4.87 volts for more than 1 second...TPS 1 signal is the dark blue and TPS 2 is the pink...you back probe the signal and ground and check your voltage with key ON with pedal at idle and then "pedal to the metal" !!...with throttle closed you should see .13 to .67 volts...and 4.09 to 4.87 at WOT (this is dark blue wire TPS 1). for TPS 2 pink wire you should see 4.3 to 4.8 volts throttle closed and .13 to 1.0 volts at WOT !!

 

Echoing what others said.

You have the following elements in the system:

- Accelerator pedal, with accelerator pedal position sensor (APP sensor) bolted on, 3x potentiometer circuit
- Throttle actuator
- Throttle position sensor (TPS), 2x potentiometer circuit
- Throttle actuator control (TAC) module, controls all of the above
- Wiring for all the above
- The throttle body itself, with a throttle plate, holds the actuator and throttle position sensor

So what can go wrong?

- APP (pedal) sensor out of spec. This has its own codes but it frequently throws other codes instead. No new ones made.
- TPS. New ones made! Yay!
- TAC. No new ones made.
- Actuator issue. They don't seem to sell these separately. But you can buy a working throttle body for like $75 w/ actuator and sensor
- Throttle plate sticking. It can just be so damn dirty that it sticks and causes issues. Clean the throttle body a bit. Or a lot. You may need to pull it to clean it. If you pull it, get a new gasket.
- Wiring issue.

I went through a long and really annoying time with this. My original pedal had issues, but it wasn't actually causing the codes. I replaced everything but the wiring. Replaced the pedal twice, actually. The cause, of course, was in fact the wiring. Previous owner cut it to extend it for a supercharger install, but didn't do it right.

 

A traction control issue is also related to the electronic throttle drive by wire----When you have a TC code the ECM uses the throttle angle to reduce TQ ----Any good scanner can tell you if you have a wheel speed sensor fault and which wheel is causing the fault This is not uncommon on an older car---Typically you will havve a fouled wheel speed sensor that either has a broken wire---a dirty connection or a bad sensor----Sort this out 1st If your engine is bone stock with only bolt ons there should be no reason for a reduced power mode---Only on highly modded engines you will exceed the "predicted airflow" The one exception is if you have a higher stall converter if your car is an auto trans---

 

You have a wiring issue... The wiring for that circuit runs down the drivers side of the engine (Top of the engine along the inboard side of the valve cover. The area near injector #7, the harness bends around a metal bracket. That bracket has been known to chafe / cut those wires.

Do the voltage and ground checks that C5 DIAG recommended

N O T E! The throttle control circuit DOES NOT have a chassis ground. It uses discrete PCM and TAC Module internal module grounds. "LOW REFF" So, trying to blame this on chassis grounds is a waste of time.

Find the THROTCONTROL Fuse in the eng compartment fuse box and use your voltmeter to read the two test points on TOP of the fuse. With the key ON Engine OFF, Read BOTH test points on top of the fuse to chassis ground and insure that you have full battery voltage on that fuse.

Bill

 

AGREE 100% !!...the THROTCONT fuse may even be blown !!..I believe if you remove the fuse your idle will be around 2000 RPM if you had no issues !!...and I believe the P1516 will set !!