Diagnostic Readout Box: Description and Operation

Model 129:

Model 140:

The diagnostic module (OBD II) is located in the module box (model 140) or next to the module box (model 129). Voltage is supplied from the base module (N16/1)

The diagnostic module (N59/1) monitors emission related signals and systems and indicates any recognized faults via the CHECK ENGINE malfunction indicator lamp (MIL). Simultaneously a diagnostic trouble code (DTC) is stored in the memory of the diagnostic module.

OBD = On-Board Diagnostics

For On-Board Diagnosis (OBD II), the diagnostic scope was substantially expanded. A total of 63 tests are performed. Recognized faults are stored under certain conditions (point of time, duration and frequency). Additionally, the ambient conditions at the moment the failure occurs (freeze frame data) are stored.

In addition to the known signals, the diagnostic module (OBD II) (N59/1) uses the following information for the expanded fault recognition:
- Signal from O2S 2 (after TWC) (G3/1)
- Pressure in purge line via the DM pressure sensor (B5/2).

O2S = Oxygen Sensor
TWC = Three-Way Catalytic converter
DM = Diagnsotic Module


DM Pressure Sensor (B5/2) and Purge-Flow Switchover Valve (Y27/6)

Model 129:

Model 140:

The DM (diagnostic module) pressure sensor (B5/2) is located on the left wheelhousing at the component compartment wall. The sensor converts pressure values into voltage signals and transmits those to the diagnostic module. Pressure changes are recognized very quickly (approximately 5 milliseconds).

The DM pressure sensor (B5/2) measures either the absolute pressure in the intake manifold or, if the purge-flow switchover valve (Y27/6) is activated, the pressure in the line between the charcoal canister and the purge control valve (Y58/1).

Function Diagram:

Graph:

Graph of DM pressure sensor (B5/2) signal output voltage (U[V]) versus absolute pressure (Pabs in bar) at 5 V supply voltage.


O2S 2 (after TWC) (G3/1)

Model 129:

Model 140:

The sensor is installed in the exhaust system after the catalytic converter. In construction and function, it is identical to O2S 1 (G3/2) before the TWC.

The signal from the O2S 2 (after TWC) (G3/1) is used by the diagnostic module to monitor the efficiency of the catalytic converter. In addition, the signal is required in the engine control module (HFM-SFI) for the operation of the dual oxygen sensor system.

The output of the oxygen sensor heater is 18 W.

O2S = Oxygen Sensor
TWC = Three-Way Catalytic converter

Block Diagram Diagnostic Module (OBD II) (N59/1):

OBD II Fault Recognition

The diagnostic module recognizes faults as follows:

- Fault reports
from the following control modules via the controller area network (CAN):
- HFM-SFI control module (N3/4)
- CC/ISC control module (N4/3) or EA/CC/ISC control module (N4/1).

EA = Electronic Accelerator
CC = Cruise Control
ISC = Idle Speed Control

- Fault path tests
Under specified operating conditions certain control paths are checked e.g. for short circuit, open circuit, implausible signals and illogical combinations.

- Logic chains
The diagnostic module triggers test cycles for:
- air injection,
- exhaust gas recirculation,
- camshaft timing adjuster,
- charcoal canister purging,
- transmission upshift delay.


Model Coding
The diagnostic module (OBD II) is supplied in one version. Model and engine adaptation takes place via the ground connection on pins 7, 8 and 10.


Diagnostic Trouble Code (DTC) Readout
The diagnostic module (OBD II) (N59/1) uses two different plug connectors for the diagnostic trouble code (DTC) readout. The DTC's can be read selectively as follows:





- Readout with Hand-Held Tester (HHT) via data link connector (DTC readout) (X11/4) (readout with Impulse counter scan tool is no longer possible).

X11/22 - Model 129:

X11/22 - Model 140:

- Readout with a Generic Scan Tool via diagnostic module (OBD II) generic scan tool connector (X11/22) (Standard communication corresponding to SAE-standard, ISO 9141 CARB).
According to regulatory requirements, DTC's can be read with a generic scan tool (readout via the pushbutton switch with LED has been eliminated).

Note: During the DTC readout, the CHECK ENGINE MIL is continuously on.

MIL = Malfunction Indicator Lamp


Function of DTC Memory

General
The fault storage and processing takes place in a RAM (Random Access Memory). When disconnecting the battery, the contents of the memory are erased.

If, during a test performed by the diagnostic module (OBD II), a fault is present without interruption for a specified time, it is stored together with the relevant freeze frame data.

A recognized fault with its freeze frame data is stored only twice - at its first and last occurrence. If a fault occurs again, the second entry is overwritten and the number of occurrences is counted.

Testing is permitted to begin approximately 10 seconds after the engine starting procedure has ended (message from engine control module HFM-SFI).


Erasing DTC Memory
The DTC memory is cleared with the Hand-Held Tester (HHT) or the generic scan tool. This will also reset the entries for the first and last occurrence of a fault.

After clearing the memory, disconnect the Hand-Held Tester or the generic scan tool (or give the "end" command) and turn the ignition off for approximately 5 seconds, so that the DTC memory can be overwritten.


Freeze Frame Data
In compliance with the SAE communication standard, the fault which first required the CHECK ENGINE MIL to be turned on is associated with freeze frame data. This association can only be overwritten once by the following failures: DTC P0_300, P0_30i (ignition misfire or combustion failure) and DTC P0_200, P1_170, P0_170 (fuel injection).

The following freeze frame data are stored:
- Diagnostic trouble code (DTC),
- Vehicle speed,
- RPM,
- Throttle valve position,
- Engine coolant temperature (ECT),
- Intake manifold pressure (MAP),
- Self-adaptation value,
- Intake air temperature (IAT),
- Operating conditions,
(O2S control ON/OFF, secondary air injection [AIR], idle speed control [ISC], deceleration shut-off, wide open throttle [WOT]),
- Elapsed mileage until malfunction occurred (no SAE standard),
- Frequency (how often malfunction occurred),
- Time since start (no SAE standard)
- Engine load condition
- Ignition timing angle


CHECK ENGINE Malfunction Indicator Lamp (MIL)





The CHECK ENGINE MIL (A1e26) is supplied with voltage directly from the base module (N16/1) and is illuminated via a ground signal from the diagnostic module. As a functional check, the MIL illuminates for a maximum of 30 seconds when switching on the ignition and up to an engine speed of approximately 500 rpm. If there are no malfunctions, the diagnostic module interrupts the ground signal to the lamp and the lamp goes out.


Activation of CHECK ENGINE MIL
Actuation scenario:
1. The requirement to switch on the CHECK ENGINE MIL is set depending on type of fault. Faults are classified into four categories:
- if the same fault occurs on two consecutive trips,
- if a fault is recognized during a single "performed" test,
- if the same fault is recognized during two consecutively "performed" tests,
- immediately when a fault is recognized.
2. After ignition OFF, the switching-on requirement is stored in the DTC memory (ignition must be turned off at least approximately 5 seconds).
3. With the next operation of the vehicle (ignition ON), if the switching-on requirement is set, the CHECK ENGINE MIL is actually switched on.

Definition: "Performed" test
A "performed" test is a specific test that is designed to verify the function or operation of a circuit or system. The test is not a "performed" test unless the test has been fully completed. Thus, the test must be fully completed at least once between ignition ON and ignition OFF (one trip). Therefore, two "performed" tests can only be obtained in two trips.


DTC Memory Storage Enablement
If the DTC memory is erased, the memory storage enablement is switched off - no DTCs may be stored until the storage enablement is switched on again. The DTC memory storage enablement is switched on again only after all tests are "performed". That is, each test must be fully performed (at least as many times as would be required to activate the CHECK ENGINE MIL if a failure were present) before the DTC memory is able to store any codes.
Exception: DTC P0_300, P0_30i (ignition or combustion misfire) and P0_200, P1_170, P0_170 (fuel injection) will activate the CHECK ENGINE MIL immediately.

Notes for repairs: If the diagnostic module has switched to fault readout mode, no faults (DTC's) are stored. An O2S fault may be stored if the exhaust system has a leak.


Note for testing the O2S, DTC P0_132 to P1_138
The sensor signal is evaluated in the diagnostic module. It must be less than approximately 1280 mV and must change constantly, with the O2S at operating temperature.
For evaluation, the diagnostic module uses the following conditions:
- "O2S heated"
Message from the engine control module via CAN, if the sensor heater current is approximately 0.2-2.0 A.
- "Exhaust gas hot"
Information is produced in diagnostic module if, with the O2S control activated, the air mass and the engine speed exceeded a certain threshold.
- "TWC hot"
Message from the engine control module via CAN, if the catalytic converter temperature rose above approximately 350 °C.


Listing of Diagnostic Trouble Codes (DTC's)/Possible Causes

P0_101 - P0_116:

P0_125 - P0_134:

P0_135 - P0_200:

Testing of ignition misfire / combustion malfunction DTC P0_300 to P0_3XX

Note for testing of ignition misfire
The engine control module checks the function of the ignition groups and ignition output stages at engine operating temperature in all load and engine speed ranges, via the primary voltage pattern. After 4 consecutive faults, the fuel to the affected cylinder is shut off and a message is sent to the diagnostic module via CAN. In addition to this protective measure, to assist in diagnosis, the engine control module counts the number of ignition misfires within 200 engine revolutions

This number, as well as the affected cylinder, is reported to the diagnostic module via CAN. This count is continuous, even if the fuel is already shut off.

Note for testing of combustion malfunction
The diagnostic module evaluates the engine speed signal (TNA) for uniformity at each engine revolution. Combustion misfires are recognized by unusual engine torque fluctuations.

Note: The XX characters shown in the following listings will be replaced with a number, identifying the specific cylinder having the problem.

P0_3XX:

P0_3XX:

P0_325 - P0_341:

P0_400 - P0_412:

P0_420 - P0443:

continued:

P0_500 - P0_510:

P0_600 - P1_170:

P1_335 - P1_340:

P1_341 - P1_443:

P1_444 - P1_700:

P1_701 - P1_741:

P1_750: