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It doesn't work like that. It's continuously variable, based on basically everything.
Quoth GM:" The ECM determines the drivers intent and then calculates the appropriate throttle response. The ECM achieves throttle positioning by providing a pulse width modulated voltage to the TAC motor."
I think this would be more productive if you described what it's doing or not doing now.
Have 5vref to TP1/TP2 now? Do you get valid-looking sensor values in the scanner for TP1/TP2 now? Does the throttle still not work?
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Is it setting any current DTCs?
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Tuner in Training
The pedal seems to work fine. I have nothing at all at the throttle body. No 5v ref. Nothing to TP1 or TP2. Nothing to any of the pins at the throttle body connector.
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Why do you still have no 5vref? Did you move the wire? Where did you move it to? Did you verify the pin you moved it to was supplying a good 5v? The TAC motor section is going to freak out and refuse to show up to play if there's no valid readings coming back from TP1/TP2. If it can't tell where the blade is it will just give up.
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Tuner in Training
I pulled 5v from C3-15. I have 5v on the blue wire at the throttle body. But nothing else. I am afraid the wiring harness is messed up. When I pulled off the back shell there were 3 in terminated black wires under there. I found one of them was for the cam position sensor. But I haven?t been able to locate the other 2. I am sure one of them is for the Big ground where the big blue spade connector is. But not sure which one. This is a nightmare.
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There shouldn't be anything else at the throttle body connector if you're just checking voltages with key-on.
Pins A & B, TAC Motor Controls, are open circuit unless/until the ECM commands a throttle position change. There should be a brief blip of positive voltage right at key-on, and then nothing until it wants something to happen.
Pin C should be constant ground at all times, unless the ECM is unplugged.
Pins D & F are sensor returns back to the ECM, and will have no voltage with the TB connector unplugged.
Pin E is the 5vref.
So, if you have nothing there except the 5v, that's pretty much exactly what I'd expect to find with a plain voltmeter when everything is working properly.
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Tuner in Training
I have confirmed I have 5v to the blue wire at the throttlebody. I have scanned the car, and get the folloeing readings
Throttle position sensor 0.0v (no matter where the throttle is)
Throttle position (SAE) 100% ( no matter where the throttle is)
pedal position 4.69v (it will sweep when depressed)
the following is the only DTC
0x7EA: U0100 - Lost Communication With ECM/PCM A (Permanant)
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Scroll down to the bottom. 3 days unlimited access to the full service manuals for $20.
I can't copy/paste/edit plain text & screencap wiring diagrams for everything you might possibly need to figure this out. Pinouts are a special pain in the ass, as they're in a table format that has to be pasted into a text editor and then line breaks/spacing manually changed to make a readable list here on the forum. You need to do what I said in the beginning, check every. single. wire. in the ECM connectors and verify that each one is going to where it's supposed to. Print out the ECM pinout list and check each one off when you trace it, and write in the non-GM wire colors the harness builders used.
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Tuner in Training
Okay I went through the wiring harness. All wires are where they should be. There were 2 wires on the APP that were crossed. I fixed that. Following are the readings are what I got on my multimeter.
A) 12.5v
B) 12.5v
C) continuity to ground
D) 5.05v
E) 5.05v
F) 1.74v
Is my computer bad?
I would like to thank everyone for their help.
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Tuner in Training
Also I back pinned all of the pins on the throttle body. And got no deviation at the throttle body when pressing the pedal Or moving the throttle blade by hand.
The pedal seems to be working properly
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I would suspect the aftermarket throttle body before the ECM. However, you should not have any voltage at either TAC A or B, except for a brief blip at key-on. After it does the initial self test those should be zero volts, no continuity to ground.
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Throttle Actuator Control (TAC) System Description
Purpose
The throttle actuator control (TAC) system delivers improved throttle response and greater reliability and eliminates the need for mechanical cable. The TAC system performs the following functions:
? Accelerator pedal position sensing
? Throttle positioning to meet driver and engine demands
? Throttle position sensing
? Internal diagnostics
? Cruise control functions
? Manage TAC electrical power consumption
The TAC system includes the following components:
? The accelerator pedal position (APP) sensors
? The throttle body assembly
? The engine control module (ECM)
Accelerator Pedal Position (APP) Sensor
The accelerator pedal contains 2 individual accelerator pedal position (APP) sensors within the assembly. The APP sensors 1 and 2 are potentiometer type sensors each with 3 circuits:
? A 5-volt reference circuit
? A low reference circuit
? A signal circuit
The APP sensors are used to determine the pedal angle. The engine control module (ECM) provides each APP sensor a 5-volt reference circuit and a low reference circuit. The APP sensors provide the ECM with signal voltage proportional to the pedal movement. The APP sensor 1 signal voltage at rest position is less than 1 volt and increases as the pedal is actuated. The APP sensor 2 signal voltage at rest position above 4 volts and decreases as the pedal is actuated.
Throttle Body Assembly
The throttle assembly contains the following components:
? The throttle blade
? The throttle actuator motor
? The throttle position (TP) sensor 1 and 2
The throttle body functions similar to a conventional throttle body with the following exceptions:
? An electric motor opens and closes the throttle valve.
? The throttle blade is spring loaded in both directions and the default position is slightly open.
? There are 2 individual TP sensors within the throttle body assembly.
The TP sensors are used to determine the throttle plate angle. The TP sensors provide the engine control module (ECM) with a signal voltage proportional to throttle plate movement. The TP sensor 1 signal voltage at closed throttle is above 4 volts and decreases as the throttle plate is opened. The TP sensor 2 signal voltage at closed throttle is below 1 volt and increases as the throttle plate is opened.
Engine Control Module
The engine control module (ECM) is the control center for the throttle actuator control (TAC) system. The ECM determines the drivers intent and then calculates the appropriate throttle response. The ECM achieves throttle positioning by providing a pulse width modulated voltage to the TAC motor.
Modes of Operation
Normal Mode
During the operation of the throttle actuator control (TAC) system, several modes or functions are considered normal. The following modes may be entered during normal operation:
? Minimum pedal value--At key-up, the engine control module (ECM) updates the learned minimum pedal value.
? Minimum throttle position (TP) values--At key-up, the ECM updates the learned minimum TP value. In order to learn the minimum TP value, the throttle blade is moved to the closed position.
? Ice break mode--If the throttle is not able to reach a predetermined minimum throttle position, the ice break mode is entered. During the ice break mode, the ECM commands the maximum pulse width several times to the throttle actuator motor in the closing direction.
? Battery saver mode--After a predetermined time without engine RPM, the ECM commands the battery saver mode. During the battery saver mode, the TAC module removes the voltage from the motor control circuits, which removes the current draw used to maintain the idle position and allows the throttle to return to the spring loaded default position.
Reduced Engine Power Mode
When the ECM detects a condition with the TAC system, the ECM may enter a reduced engine power mode. Reduced engine power may cause one or more of the following conditions:
? Acceleration limiting--The ECM will continue to use the accelerator pedal for throttle control, however, the vehicle acceleration is limited.
? Limited throttle mode--The ECM will continue to use the accelerator pedal for throttle control, however, the maximum throttle opening is limited.
? Throttle default mode--The ECM will turn OFF the throttle actuator motor and the throttle will return to the spring loaded default position.
? Forced idle mode--The ECM will perform the following actions:
- Limit engine speed to idle by positioning the throttle position, or by controlling the fuel and spark if the throttle is turned OFF.
- Ignore the accelerator pedal input.
? Engine shutdown mode--The ECM will disable fuel and de-energize the throttle actuator.
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Note that if it detects certain problems, it kills all throttle controls, and you'd get symptoms exactly as you're seeing - no throttle movement. It may be that it just doesn't know what to do with the throttle body you're using.
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1. Inspect the throttle body for the following conditions:
? A throttle blade that is NOT in the rest position
? A throttle valve that is binding open or closed
? A throttle blade that is free to move open or closed WITHOUT spring pressure
⇒ If a condition is found, replace the throttle body assembly.
Note: Disconnecting the throttle body harness connector causes additional DTCs to set.
2. Ignition OFF, disconnect the harness connector at the throttle body.
3. Ignition ON, verify that a test lamp does not illuminate between motor control 1 circuit terminal B and ground.
⇒ If test lamp illuminates, test the motor control circuit for a short to voltage. If the circuit tests normal, replace the ECM.
4. Ignition ON, verify that a test lamp does not illuminate between motor control 2 circuit terminal A and ground.
⇒ If the test lamp illuminates, test the motor control circuit for a short to voltage. If the circuit tests normal, replace the ECM.
5. Ignition ON, verify that a test lamp does not illuminate between motor control 1 circuit terminal B and B+.
⇒ If the test lamp illuminates, test the motor control circuit for a short to ground. If the circuit tests normal, replace the ECM.
6. Ignition ON, verify that a test lamp does not illuminate between motor control 2 circuit terminal A and B+.
⇒ If the test lamp illuminates, test the motor control circuit for a short to ground. If the circuit tests normal, replace the ECM.
7. Ignition OFF, allow sufficient time for the ECM to completely power down. Connect a DMM between the motor control 1 circuit terminal B and ground.
Note: When measuring peak voltage, ensure that the DMM is on the proper voltage scale and that the response time is set to 1 ms.
8. Measure for B+ on the motor control 1 circuit terminal B as the ignition is turned ON.
⇒ If the peak voltage is not within 1 volt of B+, test the circuit for an open/high resistance. If the circuit tests normal, replace the ECM.
9. Ignition OFF, allow sufficient time for the ECM to completely power down.
10. Measure for B+ on the motor control 2 circuit terminal A as the ignition is turned ON.
⇒ If the peak voltage is not within 1 volt of B+, test the circuit for an open/high resistance. If the circuit tests normal, replace the ECM.
11. If all circuits test normal, replace the throttle body.
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OK, this is me again, not copy/pasting GM this time.
If you really do have ~12v at TAC A/B, constant with key-on, unplug all 3 ECM connectors and check key-on again. If it still has ~12v with no ECM, you have a harness problem. If A/B are open circuit with the ECM unplugged, you have a bad ECM.
BUT, no matter what the ECM is doing with the TAC driver circuit, TP1/TP2 should still react to blade movement when backprobing TAC D & F: "The TP sensor 1 signal voltage at closed throttle is above 4 volts and decreases as the throttle plate is opened. The TP sensor 2 signal voltage at closed throttle is below 1 volt and increases as the throttle plate is opened."
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