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Throttle Valve Body - Not learnt

 
tracey.wilkinson21
I love my Chevy Chevette!
Posts: 1
Joined: 05/14
Posted: 05/14/14 05:57 AM

I am a corvette owner in Mallorca Spain - there are no specialists here and I have had the same recurring problem for 12 months, it was intermittent, now it happens all the time.  Have been to several garages and paid for several changes - none of which have worked.  I cant drive the car at all now.

The symptom is the engine management light comes on, then the display says "service traction system" then the display says "reduced engine power" then the car starts either hopping around or it just shuts down.

The code of the problem is P2176.  The latest mechanic downloaded the right technical remedy PDF from the Chevrolet site - he did everything it told him to do and it hasn't worked - exactly the same problem.  He now suggests I change the throttle valve body.  The part is 500 bucks, I have to ship it to spain and he is not even sure it will help.  

Can anyone help?  Really want to be sure this is the solution before I go ahead...

thanks in advance
Tracey  

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wayne712222
V-6 Camaros rule!
Posts: 31
Joined: 11/13
Posted: 05/14/14 03:30 PM

i will look around. but can you post the exact year and model of your corvette..

it just makes it easier to find the exact info for your car.. there are slight variations sometimes..

DTC P2176
Circuit Description
The commanded throttle position is compared to the actual throttle position based on accelerator pedal position and possibly other limiting factors. Both values should be within a calibrated range of each other. The engine control module (ECM) continuously monitors the commanded and actual throttle positions. This DTC sets if the values are greater than the calibrated range.

DTC Descripton

This diagnostic procedure supports the following DTC:
DTC P2176 Minimum Throttle Position Not Learned
Conditions for Running the DTC
Conditions for Setting the DTC
Action Taken When the DTC Sets
Conditions for Clearing the MIL/DTC
• The ignition is ON.
• DTCs P0120, P0122, P0123, P0220, P0222, P0223 are not set.
• DTC P2176 runs once per key cycle.
• The difference between the predicted and the actual throttle position is more than a
calibrated amount.
• The above condition is met for more than 3 seconds.
• 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.
• The ECM turns OFF the MIL after 3 consecutive drive trips that the diagnostic runs and passes.

• A History DTC clears after 40 consecutive warm-up cycles in which there are no failures reported of this diagnostic or any other emission related diagnostic.



Diagnostic Aids
The throttle valve is spring loaded to a slightly open position. The throttle valve should be open approximately 20-25 percent. This is referred to as the rest position. The throttle valve should not be completely closed nor should they be open any more than the specified amount. The throttle valve should move open and to the closed position without binding under the normal spring pressure. The throttle should NOT be free to move open or closed WITHOUT spring pressure. Replace the throttle body if any of these conditions are found.

Important: Operating the throttle blade with the Throttle Blade Control function of the scan tool may cause additional DTCs to set. Do not attempt to diagnose DTCs set during this function.

The scan tool has the ability to operate the throttle control system using Special Functions. Actuate the throttle valve using the throttle blade control function located in the TAC System menu. This function will operate the throttle valve through the entire range in order to determine if the throttle body and system operate correctly.

Check for the following conditions:
• Use the J 35616 Connector Test Adapter Kit for any test that requires probing the ECM harness connector or a component harness connector.
• Poor connections at the ECM or at the component--Inspect the harness connectors for a poor terminal to wire connection. Refer to Testing for Intermittent Conditions and Poor Connections for the proper procedure.
• For intermittents, refer to Testing for Intermittent Conditions and Poor Connections .  

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wayne712222
V-6 Camaros rule!
Posts: 31
Joined: 11/13
Posted: 05/14/14 04:02 PM

Throttle Position {TP1 And TP2) Sensors

A pair of redundant non-adjustable potentiometers that sense throttle position. The TP 1 sensor signal varies from 4.5 volts at closed throttle to 0.5 volts at maximum throttle opening (decreasing voltage with increasing throttle position). The TP 2 sensor signal varies from 0.5 volts at closed throttle to 4.5 volts at maximum throttle opening (increasing voltage with increasing throttle position). Failure of one TP sensor will set a DTC and the ECM will limit the maximum throttle opening to 35%. Failure of both TP sensors will set a DTC and cause the throttle actuator control to be disabled, and the spring-loaded throttle plate will return to the default 15% position (fast idle). Located on the throttle body.
Accelerator Pedal Position (APP1 And APP2) Sensors

A pair of redundant non-adjustable potentiometers that sense accelerator pedal position. The APP 1 sensor signal varies from 0.5 volts at the released pedal position to 3.5 volts at maximum pedal depression (increasing voltage with increasing pedal position). The APP 2 sensor signal varies from 1. 5 volts at the released pedal position to 4.5 volts at maximum pedal depression (increasing voltage with increasing pedal position, offset from the APP 1 sensor signal by 1.0 volt). The ECM interprets an accelerator pedal position of 80% or greater as a request for wide-open throttle. Failure of one APP sensor will set a DTC and the ECM will limit the maximum throttle opening to 35% Failure of both APP sensors will set a DTC and cause the throttle actuator control to be disabled, and the spring loaded throttle plate will return to the default 15% position (fast idle) Located on the accelerator pedal assembly.  

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wayne712222
V-6 Camaros rule!
Posts: 31
Joined: 11/13
Posted: 05/14/14 04:18 PM

Throttle Learn Description

The engine control module (ECM) learns the airflow through the throttle body to ensure the correct idle. The learned airflow values are stored within the ECM. These values are learned to adjust for production variation and will continuously learn during the life of the vehicle to compensate for reduced airflow due to coking. Anytime the throttle body airflow rate changes, for example due to cleaning or replacing, the values must be relearned
.
A vehicle that had a heavily coked throttle body that has been cleaned or replaced may take several drive cycles to learn out the coking. To accelerate the process, the scan tool has the ability to reset all learned values back to zero. A new ECM will also have values set to zero. The idle may be unstable or a DTC may set if the learned values do not match the actual airflow.




Throttle Learn Description

The engine control module (ECM) learns the airflow through the throttle body to ensure the correct idle. The learned airflow values are stored within the ECM. These values are learned to adjust for production variation and will continuously learn during the life of the vehicle to compensate for reduced airflow due to coking. Anytime the throttle body airflow rate changes, for example due to cleaning or replacing, the values must be relearned
.
A vehicle that had a heavily coked throttle body that has been cleaned or replaced may take several drive cycles to learn out the coking. To accelerate the process, the scan tool has the ability to reset all learned values back to zero. A new ECM will also have values set to zero.
The idle may be unstable or a DTC may set if the learned values do not match the actual airflow.

Conditions for Running the Throttle Learn Procedure
With Scan Tool - Reset Procedure
Without Scan Tool - Learn Procedure
Throttle Learn
With Scan Tool - Reset Procedure

1. Ignition ON, engine OFF, with a scan tool, perform the Idle Learn Reset in Module Setup.

2. Start the engine, monitor the TB Idle Airflow Compensation parameter. The TB Idle Airflow Compensation value should equal 0 percent and the engine should be idling at a normal idle speed.

3. Clear the DTCs and return to the diagnostic that referred you here.


Without Scan Tool - Learn Procedure

Important: Do NOT perform this procedure if DTCs are set

1. Start and idle the engine in PARK for 3 minutes.

2. With a scan tool, monitor desired and actual RPM.

3. The ECM will start to learn the new idle cells an
d Desired RPM should start to decrease.

4. Ignition OFF for 60 seconds.

5. Start and idle the engine in PARK for 3 minutes.

6. After the 3 minute run time the engine should be idling normal. If the engine idle speed has not been learned the vehicle will need to be driven at speeds above 70 km/h (44 mph) with several decelerations and extended idles.

7. After the drive cycle, the engine should be idling normally.
If the engine idle speed has not been learned, turn OFF the ignition for 60 seconds and repeat step 6

8. Once the engine speed has returned to normal, clear DTCs and return to the diagnostic that referred you here.  

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wayne712222
V-6 Camaros rule!
Posts: 31
Joined: 11/13
Posted: 05/14/14 04:33 PM

this chart is not for a GM.. but it shows the data you need to reference with a scan tool...

see the TP1 and TP2.. thats for the throttle position sensor on the throttle body.
see the APP1 and APP2.. thats for the sensor on the accelerator pedal.

you will also want to look farther down the list at the throttle actuator control percentage..

you might want to print that chart.. write the values from the scan tool down on each line.. at idle.. and a second time at a steady 2500 RPMS..

if you list a year.. and exact model/engine.. i might be able to find a wiring diagram..

the APP sensors and the TP sensors are 3 wires..  a power.. a ground and variable voltage out..  if you loose a ground connection...  you could have all kinds of issues..  

Obd2scandatachart Zps65411833  

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