State Emissions Test

threw a po128 ??? Doesn't throw code's ,it stores code's . P0128 code does not tell you to replace the sensor either . With every code comes a diagnostic test procedure listed in a factory info. manual .
DTC P0128: Engine Coolant Temperature (ECT) Below Thermostat Regulating Temperature
The purpose of this diagnostic is to analyze the performance of the thermostat, by using the ECT sensor to determine if the engine coolant will increase at the correct rate, and also meet the calibrated target temperatures under various operating conditions. The ECM uses the start-up ECT and the start-up intake air temperature (IAT) to begin the diagnostic calculation. The air flow into the engine is accumulated, and vehicle speed, distance, and engine run time are also factored in to determine if the ECT does increase normally and reach the calibrated target temperatures.
Diagnostic Aids
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DTC P0128 occurring with insufficient vehicle interior heating is an indication of improper thermostat operation.

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Corrosion in the ECT sensor terminals or the ECT harness connector results in a greater voltage on the ECT sensor signal circuit, which is interpreted by the ECM as a colder ECT.

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A slight to moderate resistance in the ECT sensor signal circuit or low reference circuit will affect this diagnostic. This condition results in a greater voltage on the ECT sensor signal circuit, which is interpreted by the ECM as a colder ECT.

Circuit/System Verification

1. Ignition OFF, inspect the cooling system surge tank for the proper coolant level. Refer to Cooling System Leak Testing and Cooling System Draining and Filling .
2. Ignition OFF for 8 hours or greater.
3. Ignition ON, observe the scan tool ECT Sensor and IAT Sensor parameters. The ECT, IAT and ambient temperatures should be within 15?°C (27?°F) of each other.
Important: A critical analysis of the operation of the thermostat is necessary to properly diagnose this DTC.

4. Verify the proper heat range, and the operation of the thermostat. Refer to Thermostat Diagnosis .
5. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the ECT sensor.
2. Ignition OFF for 90 seconds, test for less than 5 ohms between the low reference circuit terminal B and ground.
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If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.

3. Ignition ON, verify the scan tool ECT Sensor parameter is colder than -39?°C (-38?°F).
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If warmer than the specified range, test the signal circuit terminal A for a short to ground. If the circuit tests normal, replace the ECM.

4. Install a 3A fused jumper wire between the signal circuit terminal A and the low reference circuit terminal B. Verify the scan tool ECT Sensor parameter is warmer than 149?°C (300?°F).
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If colder than the specified range, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM.

5. If the circuits test normal, test or replace the ECT sensor.

Is this you instrument cluster? vtraudt image
If so, top left would be coolant temperature warning light.

What is the coolant temp gauge reading?

I would suspect faulty coolant temp sensor.
Also check if your coolant reservoir sensor (plugged into the bottom of you coolant tank) is plugged in (I often forget to plug it back in; the retainer also easily breaks and the plug can slip out).

www.kraftwerkturbo.com
www.regulatorfix.com

The crank shaft position sensor is to tell the cpu when to allow spark at the right time. IT normally works or it doesn't. Lack of take power for take off can be associated with low fuel pressure for the injectors and MAF/MAF sensor faults.. have a pressure test done on the fuel system to check for regulator failure.

yeah the price sounds about right emissions parts on audis are really expensive. you could always shop around online and try to find a used one that is still in good shape with no cracks. I know cause i own Audi A6 2.7t 2001 and also work on it myself.

Replace cat. The mechanic was correct.

P0116 Engine Coolant Temperature Sensor Performance, This DTC is usually set by a defective coolant temp. sensor or the related wiring. However, there is an old service bulletin. TSB#18-017-03 that calls for replacement of the Powertrain Control Module to repair this condition.

P0116 - Engine coolant temperature circuit range/Performance problem

P0118 - Engine coolant temperature circuit/High input

P0456 - EVAP leak monitor/Small leak detected

The following web site list all codes


http://www.2carpros.com/trouble_codes

Hi, the sensor on the engine (right at the rear end of the cylinder head) has two separate outputs. One drives the temperature gauge and the other provides data for the engine control unit. The output for the engine control unit is almost certainly faulty and the sensor will need to be replaced. It isn't an expensive item and's not time consuming to replace (1/2 hr) - so you could ask Audi to do it for you when they replace the ignition coils.
Hope that helps Matt..

The light is comming back on because you have a problem in the emission control system, without the code I can't help you any further, one note it takes the system a couple of days to go through self test before it decides there is a problem, that is why the delay.

what i used to do is pour a small bottle of rubbing alcohol in the gas tank....this mixture burns very hot so it will clean everything out thus burning all the gas particles off......i used to do this in a 1988 mustang gt that ran real rich because of performance parts and i couldnt ever get it to pass the tests....also try o2 sensors as well as possibly map sensor if equipped...this could be the problem....
temp gauge not working? check wiring and also check tempature sending unit and block temperature sensor.