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Old August 4th, 2001, 07:44   #1
Turbo Steve
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Join Date: Jan 2000
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Default Engine Control Management - 101

Here's a Reader's Digest version of what the computer does on our TDI's (hope you don't mind a few acronyms):

The 1.9 liter ALH engine is equipped with the Turbo Direct Injection System (TDI) that features engine controls which closely resemble those of Volkswagen's gasoline engines.

Example - Our TDI diesel engine is managed by a computerized Engine Control Module (ECM) that is largely patterned after Bosch's Motronic ME 7.5 ECM, which monitors the sophisticated 1.8L 4-cylinder turbo engine and is called a Direct Fuel Injection (DFI) ECM (J248).

(Note - ECM is the same system with a similar term as Engine Control Unit (ECU) and both acronyms can be used interchangeably.)

The DFI computer in our TDI is accessed in the same manner as other VW's are, through an On-Board Diagnostic system called or known as "OBD II," using a Data Link Connector (DLC) plug to check the status of the DFI computer. This DLC outlet plug is located by the driver's left knee, if he/she were in a seated position behind the steering wheel.

Also, the Bosch Motronic 5.9.2 governs the AEG 2.0L 4-cylinder and the Motronic ME 7.1 controls the AFP 2.8L 6-cylinder engine.

The TDI Engine Management System combines very technical computerized control of the diesel fuel and obviously emissions, with continual system monitoring and periodic diagnostic checks. An exhaust-driven turbocharger with a nifty intercooler work hand-in-hand to produce a more efficient combustion out of less fuel. Part of this also results from the specially designed piston / combustion chamber and the aluminum cylinder head, which result in reduced engine noise and increased power.

* . * . * The turbo's boost pressure is largely regulated by the signals the computer receives from the Intake Air Temperature (IAT) Sensor, the Mass Air Flow (MAF) Sensor, and the outside air temperature as indicated by the Barometric Pressure Sensor (BARO). * . * . *

The go-pedal is also included in the ECM mix via a potentiometer, which eliminates the need for an accelerator cable. The more common-term of sending this signal to the ECM is "Drive By Wire" (DBW). The computer also controls the cruise control and all glow plug functions.

On the TDI engine, diesel fuel is metered according to engine load and RPM's. For example, when the ignition key is switched on and/or the fuel cutoff valve opens to allow the injection pump to pressurize fuel for the injectors, the ECM receives the engine RPM signal from the Engine Speed Sensor (ESS) and load information from the Throttle Position Sensor (TPS).

These signals are then modified by the Engine Coolant Temperature (ECT) Sensor, the Mass Air Flow (MAF) Sensor, and the Fuel Temperature Sensor (FTS).

The ECM also uses input from the above sensors to determine the correct amount of injection (quantity) and when to inject it (quality of ignition burn). Also, each individual injector sends a generated output signal back to the #3 Injector / Needle Lift Sensor (NLS) and the Cold Start Valve (CSV) at the correct time. The ECM monitors the operation of the CSV through a signal received from the Needle Lift Sensor attached to Injector #3 and again makes corrections as required in order to keep all 4 injectors evenly balanced and working together as one.

The computer also monitors the operation of the Fuel Quantity Adjuster (FQA) via a signal it receives from the Modulating Piston Displacement Sensor (MPDS) and naturally makes any adjustments needed to the fuel quantity as required.

Furthermore, in order to prevent possible damage from simultaneously applying the brake / clutch / go-pedals, these three systems with pedals continually send a signal to the ECM of their respective positions. Note - The computer also uses this input for monitoring the Cruise Control (CC) System.

When the TDI engine is shut-off, the computer sends a signal to the intake manifold's Change-over Valve (COV), which is basically a butterfly style throttle valve which closes and effectively blocks the flow of air to the engine. By using a Change-over Valve during the shut-down cycle of the engine, any abruptness or run-on is eliminated and the engine smoothly comes to a halt. If you listen carefully, you can hear the valve reopen once the engine stops running.

TDI's also have two warning lights in the Instrument Cluster Panel (ICP) to advise the driver of the status of the computer.

1. The Glow-plug Indicator Light (GIL) is supposed to operate when the key is first turn to the "on" position, in order to indicate the need to wait for the glow plugs to pre-heat the four combustion chambers.

2. The more-common Malfunction Indicator Light (MIL) will come on briefly during startup of the engine when the ECM does a diagnostic test and will only stay on if there is a failure of a monitored component.

In some cases, it's entirely possible for the MIL and GIL warning indicators to remain lit at the same time.

As far as diagnosing and repairing of the complex nature of the TDI Engine Management System, this requires the use of special VW Scan Tools like the VAG 1551 or VAG 1552.

Aftermarket software is also available from Uwe Ross at Uwe.Ross@pobox.com and can access the Diagnostic Trouble Codes (DTC or P-codes).

In summary, the computer receives data from numerous input devices called sensors and modifies the data according to it's software program. It then relays the altered data to various output components which put into action the anticipated desired result.

Here is a short list of Input Sensors:

* Needle Lift sensor (G-80)
* MAF Sensor (G-70)
* IAT Sensor (G-72)
* RPM Sensor (G-28)
* Engine Coolant Temperature Sensor (G-62)
* MAP Sensor (G-71)
* Throttle Position Sensor (G-79)
* Fuel Temperature Sensor (G-81)
* Modulating Piston Displacement Sensor (G-149)
* Vehicle Speed Sensor

Output Components

* Engine Glow Plugs (Q-6)
* Coolant Glow Plugs (Q-7)
* EGR Vacuum Regulator Valve (N-18)
* Intake Manifold Change-over Valve (N-239)
* Injection Pump Quantity Adjuster (N-146)
* Injection Pumpís Timing
* Injection Pump Fuel Cut-off Valve (N-109)
* Injection Pump Cold Start Injector (N-108)
* Instrument Cluster

(Bentley Publishers 2000 TDI Manual for Jettas and Golfs also has plenty of pics and more info on this subject, which were used to assist in compiling this article. See also sections 2-2 thru 2-5.)


* Turbo Direct Injection System (TDI)

* Engine Control Module (ECM)

* Direct Fuel Injection (DFI) of ECM (J248)

* Engine Control Unit (ECU)

* On-Board Diagnostic System (OBD II)

* Data Link Connector (DLC)

* Intake Air Temperature (IAT) Sensor

* Mass Air Flow (MAF) Sensor

* Barometric Pressure Sensor (BARO)

* Drive by Wire (DBW)

* Engine Speed Sensor (ESS)

* Throttle Position Sensor (TPS)

* Engine Coolant Temperature Sensor (ECT)

* Fuel Temperature Sensor (FTS)

* Needle Lift Sensor (NLS)

* Cold Start Valve (CSV)

* Fuel Quantity Adjuster (FQA)

* Modulating Piston Displacement Sensor (MPDS)

* Cruise Control (CC) System

* Change-over Valve (COV)

* Instrument Cluster Panel (ICP)

* Glow-plug Indicator Light (GIL)

* Malfunction Indicator Light (MIL)

* Diagnostic Trouble Codes (DTC or P-codes)
Turbo Steve is offline   Reply With Quote
Old August 4th, 2001, 09:58   #2
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Join Date: Jun 2001
Location: the abyss
TDI(s): 2k2 Jetta
Default Re: Engine Control Management - 101


Very informative, TS! I learned a couple of acronyms with which I hadn't previous experience. Please don't take my chuckle the wrong way, but I always bust out laughing when I have to read "acronyminous" papers [img]images/icons/wink.gif[/img]
jetmann is offline   Reply With Quote
Old March 11th, 2018, 12:48   #3
Join Date: Feb 2017
Location: NY, near NJ & PA
Default Re: Engine Control Management - 101

Is the BOSCH Motronic 5.9.2 used in all North American TDI's... as of 2002... as stated in the "A3 vs A4 engine swap" forum thread at
They are apparently coded differently between engine types (such as between the AHU and the ALH). Can they be recoded when swapping between engines? (What tool would one need to re-code?)
OllieTDIed is offline   Reply With Quote

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