Audi B6 1.9 tdi running poorly after ECU replacement, no fault codes

The following are the general instructions on the start of diagnosing any electronically controlled engine or transmission problem.

The engine and the automatic transmission (transmission control is only for automatics, engine is still computer controlled no matter the transmission type) in this vehicle are computer controlled and in most cases when a fault occurs a fault code is stored in the memory of the computer control module. There are exception to this, such as the Mass Airflow Meter and fuel pressure problems. What must be done is to have all the basic testing done such as a scan of the system for fault codes as well as a check with a live data scanner tool for engine functions that are not within range of normal, a trained technician is required to know what is correct and what isn't, then based on careful diagnostics done from a factory repair manual the correct part is replaced or the wiring repaired or the computer replaced (known as the PCM or ECM,ECU), which is very rarely the problem. Other basic checks must be done as well such as mechanical problems with the engine as well as engine state of tune and mileage on the engine. The transmission can have mechanical issues as well such as no gear engagement at all or a failed pump or other pressure related problems. Also engine mechanical problems can and do cause many drive-ability related problem such as rough idle and other symptoms.

You need the engine computer scanned for fault codes, i thank you have an ignition control problem like a module or distributor pickup coil issue. These parts whenthey fail should leave fault cdes so get them read.
Next, the check engine light will pause shortly followed by the second digit of the trouble code. For example if the check engine light blinks once and pauses followed by six blinks the trouble code number would be 16. If no code is present the check engine light will stay one constantly. To restart code gathering turn the ignition key to the "off" position, wait three minutes and turn the ignition key back "on" again without starting the engine. Remove the jumper wire once code gathering is complete. To clear code after the repairs have been made remove the negative battery cable for one minute and reconnect.

Toyota Diagnostic Connector
Toyota Code Definition Table
Code 11 Momentary interruption in power supply to ECU (electronic control unit or computer) up to 1991
Code 12 Engine revolution signal missing Code 13 Rpm signal to ecu missing above 1000 rpm
Code 14 Igniter signal to ecu missing
Code 16 A/T control signal missing from ecu
Code 21 Main oxygen sensor signal fault
Code 22 Water temperature sensor circuit fault
Code 23 and 24 Intake air temperature signal fault
Code 25 Air/fuel ratio LEAN
Code 26 Air/fuel ratio RICH
Code 27 Sub-oxygen sensor signal or heater circuit fault
Code 28 No. 2 oxygen sensor/heater signal fault
Code 31 and 32 Air flow meter circuit or Vacuum sensor signal fault Code 34 and 36 Turbo-charging pressure signal fault
Code 35 Altitude compensation sensor signal fault
Code 41 Throttle position circuit fault
Code 42 Vehicle speed sensor circuit
Code 43 No starter signal to the ecu
Code 51 AC signal on; DL contact off (in transmission shifter with diagnostic connector jumped)
Code 52, 53 and 55 Knock sensor fault Code 71 EGR system malfunction
Code 72 Fuel cut solenoid signal fault
Code 78 Fuel pump control signal fault
Code 81, 83, 84 and 85 TCM communication fault

sound more like an alternator problem

In the most cases for Audi 2.0 TDI the turbocharger is responsible for engine losing power.
The car goes in "limp home" mode!!!
After scan the EDC-15P engine control unit with a VAG or KTS -BOSCH diagnosis tool you will find this: Fault code: P1557-Turbo Boost pressure control exceeded
1. Engine stopped and ignition switch off. Check all pneumatic connections and hoses between turbocharger actuator = pressure unit for boost-pressure control, boost-pressure control solenoid valve, vacuum reservoir, EGR control solenoid valve, intake-manifold flap solenoid valve, EGR valve with throttle - part of intake manifold. Also the vacuum connection between tandem pump and brake booster. If you find something wrong replace parts. If not go to step 2.
2. Extract the hose of the turbocharger actuator = pressure unit for boost-pressure control part of turbocharger. Instead of the original hose you must place another 1 meter long hose with the same inside diameter, and then you check to inspire yourself the air from the other one extremity of this hose. The mechanical connecting rod of the turbocharger actuator must have a smooth and whole motion. If you can do that with your mouth, then you must replace the boost-pressure control solenoid valve. If you can not reach this with your mouth, then you go to step 3.
3. This is the most difficult work. The problem is that the soot particles deposits inside the turbocharger plugging the variable nozzle geometry mechanism = adjustable vanes of the turbine. If the turbocharger actuator is not able to adjust the turbine vanes the charge air pressure increase too much and ECU (engine control unit) go in "limp mode" = engine protection software. As a result the "limp home" mode engine still running until you turn the engine off (ignition switch off) and back on when the "limp mode" is deactivated, but the fault still remain in ECU memory!
4. You must be able to extract the turbo from the engine and then to disassemble the turbocharger, clean inside adjustable vanes mechanism and refit all.

In the most cases for Audi A4 1.9 TDI the turbocharger is responsible for engine losing power.
The car goes in "limp home" mode!!!
After scan the EDC-15P engine control unit with a VAG or KTS -BOSCH diagnosis tool you will find this: Fault code: P1557-Turbo Boost pressure control exceeded
1. Engine stopped and ignition switch off. Check all pneumatic connections and hoses between turbocharger actuator = pressure unit for boost-pressure control, boost-pressure control solenoid valve, vacuum reservoir, EGR control solenoid valve, intake-manifold flap solenoid valve, EGR valve with throttle - part of intake manifold. Also the vacuum connection between tandem pump and brake booster. If you find something wrong replace parts. If not go to step 2.
2. Extract the hose of the turbocharger actuator = pressure unit for boost-pressure control part of turbocharger. Instead of the original hose you must place another 1 meter long hose with the same inside diameter, and then you check to inspire yourself the air from the other one extremity of this hose. The mechanical connecting rod of the turbocharger actuator must have a smooth and whole motion. If you can do that with your mouth, then you must replace the boost-pressure control solenoid valve. If you can not reach this with your mouth, then you go to step 3.
3. This is the most difficult work. The problem is that the soot particles deposits inside the turbocharger plugging the variable nozzle geometry mechanism = adjustable vanes of the turbine. If the turbocharger actuator is not able to adjust the turbine vanes the charge air pressure increase too much and ECU (engine control unit) go in "limp mode" = engine protection software. As a result the "limp home" mode engine still running until you turn the engine off (ignition switch off) and back on when the "limp mode" is deactivated, but the fault still remain in ECU memory!
4. You must be able to extract the turbo from the engine and then to disassemble the turbocharger, clean inside adjustable vanes mechanism and refit all.

WHEN EVER YOU DISCONNECT BATTERY PCM LOSE MEMORY WHICH CAUSE POOR ENGINE PERFORMANCE.TAKE CAR TO VOLKSWAGON DEALERSHIP LET THEM REPROGRAM IT.

the simple reason for it with your fuel supply system it might have choke-up, check the fuel filter for supply, check for electriacl problem, check for ECU problem, in case for much problem you can reach trouble free to nearest authorised VW, SKODA, AUDI, dealer or service centre to sort out the problem you are facing so friend see you soon......!

Your motor probably runs in "failsafe" mode (won't go past 3000rpm in highest gear), but in that case the ECU warning light should also come on (which might also be broken ofcourse).

Try releasing and reconnecting the battery (-connectors), which should "reset" any fault-codes in the ECU and see if the TDI power is back. Please note that the "cause" of the ECU faultcodes will probably put the motor back in "failsafe" mode within minutes ! But at least you've verified that your motor runs in "failsafe" mode due to serious faultcodes in the ECU.

You should have a dealer/expert read the ECU faultcodes using VAGCOM to determine the cause. A dealer will charge something like 50~60$ for it.

Since it's a 1.9TDI my best guess is that's it a broken N75 turbo-valve (common TDI issue, replacing the part yourself will cost less than $30 and 15 minutes). When the dealer suggests a complete replacement of the Turbo-unit (quite expensive), please have a TDI-expert do an 2nd opinion ...

ecu problem! go and find someone with VAG-COM and get it checked for fault codes. glad i could help!

Your car goes in "limp mode"!!!
If you scan the EDC-15P engine control unit with a VAG or KTS -BOSCH diagnosis tool you will find this:
"Fault code: P1557 - Turbo Boost pressure control exceeded"
You must try follows if you are able to do this:
1. Engine stopped and ignition switch off. Check all pneumatic connections and hoses between turbocharger actuator = pressure unit for boost-pressure control, boost-pressure control solenoid valve, vacuum reservoir, EGR control solenoid valve, intake-manifold flap solenoid valve, EGR valve with throttle - part of intake manifold. Also the vacuum connection between tandem pump and brake booster. If you find something wrong replace parts. If not go to step 2.
2. Extract the hose of the turbocharger actuator = pressure unit for boost-pressure control part of turbocharger. Instead of the original hose you must place another 1 meter long hose with the same inside diameter, and then you check to inspire yourself the air from the other one extremity of this hose. The mechanical connecting rod of the turbocharger actuator must have a smooth and whole motion. If you can do that with your mouth, then you must replace the boost-pressure control solenoid valve. If you can not reach this with your mouth, then you go to step 3.
3. This is the most difficult work. The problem is that the soot particles deposits inside the turbocharger plugging the variable nozzle geometry mechanism = adjustable vanes of the turbine. If the turbocharger actuator is not able to adjust the turbine vanes the charge air pressure increase too much and ECU (engine control unit) go in "limp mode" = engine protection software. As a result the "limp mode" engine still running until you turn the engine off (ignition switch off) and back on when the "limp mode" is deactivated, but the fault ("Fault code: P1557 - Turbo Boost pressure control exceeded") still remain in ECU memory !!!
4. You must be able to extract the turbo from the engine and then to disassemble the turbocharger, clean inside adjustable vanes mechanism and refit all.
It is some work to do here, but after that you will be full satisfied! NO MORE "LIMP MODE"!!!
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It is a certified solution. Last year in July I made this turbocharger cleaning on my car - 2000 Audi A4 1.9 TDI 116 HP. After 25000 km my car runs like an authentic AUDI 1.9 TDI.