Electronic Modules - Design and Function: Diagnosis Volvo XC90 I

DIAGNOSTIC TROUBLE CODES (DTCS)

Diagnostic trouble codes (DTCs) are stored in the control module if the climate control module (CCM) detects a fault. Every diagnostic trouble code (DTC) has a counter which records the number of cycles which have been "fault-free" since the diagnostic trouble code (DTC) was stored. A fault which is detected in each operating cycle is defined as permanent. A fault which is detected in one or more operating cycles (although not the present one) is defined as intermittent.

An operating cycle is the period from when the ignition was switched on, remained on for at least 10 seconds and was finally switched off for at least 10 seconds.

READING AND ERASING DIAGNOSTIC TROUBLE CODES (DTCS)

Stored diagnostic trouble codes (DTCs) can be read off and erased using this function.

BLOWER FAN DIAGNOSTIC SIGNAL, VALUE

Measurement range: 0-5 V

The climate control module generates an analog signal. This is converted to a current which the power unit converts back to an analog signal. The diagnostic signal is an extremely intense signal that cannot be used when checking the blower fan.

Diagnostic trouble codes (DTCs) are stored in the control module if the climate control module (CCM) detects a fault. Each diagnostic trouble code (DTC) has a counter which records the number of operating cycles which have been fault-free since the diagnostic trouble code (DTC) was last stored. A fault which is detected in the present operating cycle is defined as permanent. A fault which is detected in one or more operating cycles (although not the present one) is defined as intermittent.

An operating cycle is the period from when the ignition has been off, then on for at least 10 seconds and finally off for at least 10 seconds.

Stored diagnostic trouble codes (DTCs) can be read off and erased using this function.

SAS DIAGNOSTIC FUNCTIONS

General

The control unit has built-in diagnostics, Volvo Diagnostics, which continually monitor the unit and the input and output signals.

Diagnostic trouble codes

If the control unit detects a fault, it stores a diagnostic trouble code. If, for any reason, a fault disappears after the diagnostic trouble code has been permanently stored in the control unit, information about the trouble code still remains in the control unit.

Reading and erasing diagnostic trouble codes

Stored diagnostic trouble codes can be read from the control unit using this facility.

Diagnostic trouble codes may be erased but only after they have been read at least once.

Reading input and output signals

Status of control unit input and output signals can be continually read using this facility.

For more information about parameters, see DESCRIPTION OF PARAMETERS (STEERING ANGLE SENSOR) .

Reading the control unit identity

VIDA identifies control units by reading the number of codes from the control unit memory. The codes contain information on the control unit as follows

1. hardware component number (control units without software)
2. software component number (control units without software)
3. software component number
4. diagnostic software component number

DIAGNOSTIC VERSIONS AND COMMUNICATION METHODS

GENERAL

Since the end of the 1980s, the control module's diagnosis has developed from detecting simple problems and storing a small amount of information to including more complicated tests and checks.

Today a large amount of information can be read out both about the detected problem as well as parameters from the control module's input and output signals.

VOLVO DIAGNOSTICS II - FIRST VERSION

Volvo Diagnostics II - first version was a new Volvo standard introduced in 1996 . This meant that control modules communicated serially in the same way, and that diagnostic functions in the different systems were designed in a similar manner.

The communication cable in the vehicle used for this communication is common to all control modules in question. The control modules are connected to the same connection in the diagnostic socket (pin 7).

The diagnostic socket is located in the passenger compartment and for certain markets it is common with the diagnostics system OBD II.

Volvo Diagnostics II, first version, was introduced in 1996 on, among others

1. Engine management system Motronic 4.4
2. Automatic transmission AW 50 42/AW 30 40/43
3. Control module Airbag SRS6.2
4. Immobilizer
5. Control module Brakes ABS 850
6. Combined instrument panel 850
7. Power seat 850/960
8. and was gradually introduced for additional systems and car models.

For certain models, the diagnostics tool for this diagnosis is still Volvo System Tester (car models from and incl. model year 1998 as well as certain systems for model year 1999).

The diagnostics tool VIDA, now replacing VADIS, is used for car models of model year 1999 and later.

Scheme 18

Volvo Diagnostics II - second version was introduced in 1999 and is a development of the first version. The major difference is that communication between the diagnostics tool and the control modules takes place via CAN-communication instead of on a communication cable.

The control modules also communicate with each other to exchange information on the CAN-net instead of via separate cables between the control modules.

This version introduced the possibility to download software to the control modules.

With the introduction of this version, the rate in the low-speed network was (LS CAN) 125 kbit/s and the rate in the low-speed network was (HS CAN) 250 kbit/s. Depending on model and model year, the speed of the network has increased with time.

The diagnostics tool VIDA, now replacing VADIS, is used for car models of model year 1999 and later.

Scheme 19

Generic Global Diagnostics (GGD) is a mutually developed diagnostics concept within the Ford company.

Communication and services are similar to Volvo Diagnostics II - first version. Communication between the diagnostics tool and control modules takes place via CAN-communication. The services that can be performed are similar.

Designation of trouble codes adheres to standard ISO/DIS 15031-6.4 and consist of a letter and six characters.

The control modules also communicate on the CAN-net with each other to exchange information.

It is also possible to download other software to the control modules.

Volvo Diagnostics, fifth version, was introduced in model XC90 model year 2005 with engine B8444S (only high-speed network) and then in model S80 (07-).

The diagnostics tool VIDA, now replacing VADIS, is used for car models of model year 2005 and later.

DIAGNOSTICS AND SERVICES

GENERAL

Scheme 20

The control module's diagnostics can perform and present the following using a connected diagnostics tool

1. Store malfunction indicator (diagnostic trouble codes) and in certain cases activate warning light or show text message. Counter that indicates how frequent the malfunction is Status indicators for the diagnostic trouble code test. Frozen values that were generated when malfunction was detected for the first time.
2. Store information about the nature of the malfunction: Counter that indicates how frequent the malfunction is Status indicators for the diagnostic trouble code test. Frozen values that were generated when malfunction was detected for the first time.
3. Erase information about malfunction and its information.
4. Present values (parameters) for different connected input signals and output signals from, e. g., components as well as other calculated values.
5. Present part number, version number, component number, etc. for both software and hardware.
6. Present and change certain special customer settings and configurations.
7. Trigger/control (activate) the connected output signals.
8. Start special built-in check programs/tester such as, e. g., calibrations of gear position sensor, quick-test of tank system.
9. Access check to limit access to certain parameters and functions. Accessible first after unlocking with, e. g., PIN-code.

Exactly what each control module's diagnostics can perform depends both on model year and system.

DIAGNOSTIC TROUBLE CODES (MALFUNCTION INDICATOR)

1. see «IDENTIFYING MALFUNCTION»(ref-476897-S09939262332012061300000)
2. see «CONDITIONS FOR DIAGNOSIS TO FIND A MALFUNCTION»(ref-476897-S40715755742012060500000)
3. see «DRIVING CYCLE/OPERATION CYCLE»(ref-476897-S24769746872012060500000)
4. see «EMERGENCY MODE, BACK-UP MODE "LIMP-HOME"»(ref-476897-S27663693762012060500000)
5. see «CLASSIFICATION OF DIAGNOSTIC TROUBLE CODES»(ref-476897-S00164631092012060500000)
6. see «DESIGNATION OF TROUBLE CODES»(ref-476897-S25392343432012060500000)
7. see «STATUS IDENTIFIER»(ref-476897-S06273113572012060500000)
8. see «COUNTER»(ref-476897-S28510117132012060500000)
9. see «FROZEN VALUES»(ref-476897-S07763065222012060500000)
10. see «ERASING DIAGNOSTIC TROUBLE CODES»(ref-476897-S08966171842012060500000)
11. see «READINESS MONITOR (CERTAIN MARKETS ONLY)»(ref-476897-S30034011482012060500000)

ERASING DIAGNOSTIC TROUBLE CODES

Stored diagnostic trouble codes (DTCs) can be read off and erased using this function. Diagnostic trouble codes (DTCs) can only be erased once all the diagnostic trouble codes (DTCs) have been read off at least once.

When erasing diagnostic trouble codes, the diagnostic trouble code's counter, status identifier as well as frozen values are also erased.

For certain systems, stored adaptions may also be reset when erasing.

Scheme 21

All control modules' diagnostics require that some form of driving cycle or operation cycle is run for diagnostics to be considered as complete. The terms driving cycle or operation cycle appear, these mean the same, they are only different designations.

Example

The illustration above shows an example of a driving cycle or operation cycle. The vehicle is started and driven (Start) , is stopped sometime and the ignition is turned off (Stop) . When the ignition is turned on again (Start) a new driving cycle starts.

A new driving cycle or operation cycle usually starts every time the ignition is turned on, which means that you should turn on the ignition, turn off the ignition, and then turn on the ignition again.

However, the condition varies from control module to control module, there are also, e. g., speed and temperature conditions, before a driving cycle or operation cycle is considered to be complete.

When a malfunction is detected and then is confirmed as a real malfunction and is stored, various counters are also stored, indicating how frequent the malfunction is. These counters use driving cycles or operation cycles as basis for updating the counters' values.

DESIGNATION OF TROUBLE CODES

The diagnostics tool VIDA shows the diagnostic trouble code in plain text according to the following example

TCM-001F Speed sensor Signal missing Permanent malfunction

This diagnostic trouble code consists of the following parts

1. Prefix for control system in question ( TCM ) to show what system the diagnostic trouble code belongs to. * If the qualifier is, e. g., "Too high signal", the control module interprets that the signal from the sensor is too high. This may mean that, e. g., the voltage is too high, current is too high, frequency is too high, or the pulse ratio (% duty) is too high, all depending on which type of signal it is. Malfunction causes may be, e. g., open circuit or short-circuiting to voltage. If the qualifier is "Too low signal", the control module interprets that the signal from the sensor is too low. Malfunction causes may be, e. g., open circuit, short-circuiting to ground, contact resistance in connections. NOTE: Information about which type of signal that the control module detects and what conditions are required to detect that a malfunction is found again in the diagnostic trouble code information.
2. Diagnostic trouble code number ( 001F ) to decide which diagnostic trouble code is stored. Number of digits in the diagnostic trouble code number may vary. *, ** If the qualifier is, e. g., "Too high signal", the control module interprets that the signal from the sensor is too high. This may mean that, e. g., the voltage is too high, current is too high, frequency is too high, or the pulse ratio (% duty) is too high, all depending on which type of signal it is. Malfunction causes may be, e. g., open circuit or short-circuiting to voltage. If the qualifier is "Too low signal", the control module interprets that the signal from the sensor is too low. Malfunction causes may be, e. g., open circuit, short-circuiting to ground, contact resistance in connections. NOTE: Information about which type of signal that the control module detects and what conditions are required to detect that a malfunction is found again in the diagnostic trouble code information.
3. Title ( Speed sensor ) is a text that shows to which component/function the diagnostic trouble code refers. * If the qualifier is, e. g., "Too high signal", the control module interprets that the signal from the sensor is too high. This may mean that, e. g., the voltage is too high, current is too high, frequency is too high, or the pulse ratio (% duty) is too high, all depending on which type of signal it is. Malfunction causes may be, e. g., open circuit or short-circuiting to voltage. If the qualifier is "Too low signal", the control module interprets that the signal from the sensor is too low. Malfunction causes may be, e. g., open circuit, short-circuiting to ground, contact resistance in connections. NOTE: Information about which type of signal that the control module detects and what conditions are required to detect that a malfunction is found again in the diagnostic trouble code information.
4. Qualifier ( Signal missing ) is used to show how the control module has perceived the signal from, e. g., the sensor, or how it detected the monitored function. In this case, the control module has perceived that the signal is missing. There a re a number of other qualifiers for, e. g., too high signal, incorrect signal, too high flow, too low flow, etc. *, **. If the qualifier is, e. g., "Too high signal", the control module interprets that the signal from the sensor is too high. This may mean that, e. g., the voltage is too high, current is too high, frequency is too high, or the pulse ratio (% duty) is too high, all depending on which type of signal it is. Malfunction causes may be, e. g., open circuit or short-circuiting to voltage. If the qualifier is "Too low signal", the control module interprets that the signal from the sensor is too low. Malfunction causes may be, e. g., open circuit, short-circuiting to ground, contact resistance in connections. NOTE: Information about which type of signal that the control module detects and what conditions are required to detect that a malfunction is found again in the diagnostic trouble code information.
5. Status ( Permanent malfunction ) to show the malfunction's status, that is, if the malfunction has been detected in the present driving cycle or not. There are two different status texts, permanent or intermittent. When the control module's diagnosis cannot decide the malfunction's status, the diagnostic trouble code is shown without status text. *

* When reading out diagnostic trouble codes using diagnostic socket with light-emitting diode, you get a three-digit flash code. Then this code is translated to a diagnostic trouble code text using the service information.

For example, if the control module flashes the code 1-2-3 from Engine control module (ECM), it can be translated to, e. g., diagnostic trouble code 1-2-3 Engine temperature sensor. Volvo Diagnostic Key and Volvo System Tester translate these flash codes directly to plain text (add a title). In these diagnostic systems it is not possible to show qualifier or status.

** For systems with diagnostic version called Generic Global Diagnostics (GGD) (adheres to standard ISO/DIS 15031-6.4) the diagnostic trouble code number consists of a letter and six characters. The letter alternatives are B, C, P and N, which means Body, Chassis, Powertrain and Network and indicate to which "function" in the vehicle the diagnostic trouble code belongs. The six following characters may consist of both letters (A-F) and digits (0-9) and indicate the component to which the malfunction refers as well as what type of malfunction. See following example.

BCM-C006A16 Multi-axial acceleration sensor. General electric malfunction. Too low voltage

CLASSIFICATION OF DIAGNOSTIC TROUBLE CODES

In principle, malfunctions can be classified in two categories, intermittent or permanent.

Permanent malfunctions.

The easiest malfunctions to identify and confirm as a malfunction are the permanent malfunctions. A permanent malfunction is a malfunction when something has "broken" and remains like that until it is repaired.

Intermittent malfunctions.

The intermittent malfunctions are, as opposed to the permanent malfunctions, are both difficult to identify and confirm. The malfunction exists but is neither active nor present all the time. The malfunction comes and goes briefly under very rare conditions.

For the intermittent malfunctions, the degree of intermittence can also be determined, that is, how intermittent the malfunction is (how often/seldom the malfunction appears).

HINT: For assessment of intermittence, stored counters are used together with the diagnostic trouble code.

Common permanent malfunction causes are

1. Open circuits or short-circuits on cables or in connectors caused by mechanical damage, vibrations, corrosion, oxidation, moisture, etc.

Common intermittent malfunction causes are

1. Loose connections or contact resistance caused by vibrations, corrosion, oxidation, moisture, etc.
2. Brief short-circuits to both ground and voltage caused by damage to cables, moisture in connectors, etc.
3. Electro-magnetic interference.

Malfunction causes may be both electrical, mechanical or related to software.

Intermittent malfunctions (or malfunctions that occur under unknown conditions) may also be malfunctions that only occur during certain operation or ambient conditions.

E. g., that the window or seat for some reason jams in its end-position when using automatic function, or that the climate control unit supplies poor heat in a certain position when it rains outside.

CONDITIONS FOR DIAGNOSIS TO FIND A MALFUNCTION

For the control module's self-diagnosis of a component or function to start and run (one or several times) special conditions must be fulfilled. Conditions for diagnosis varies depending on which component or function is to be monitored. When the diagnosis has started and is run, the signal, value or function must go above or below the limit value for the control module to detect a malfunction.

Example of conditions for the control module to start the diagnosis/test

1. Engine speed higher than 500 rpm.
2. Ignition position II.
3. Speed above 40 km/h.
4. 4th gear selected.

Example of limit values for detecting malfunction

1. Direct voltage from outside temperature sensor lower than 0.495 V for a time longer than 1 second.
2. After the engine has run for approx. 10 minutes, the control module receives an unchanged signal from the oil temperature sensor even though the signal should have changed according to a set pattern.
3. Malfunction shall be active (permanent) for at least 2 driving cycles.

Example

Scheme 22

The illustration shows an imagined scenario when a malfunction occurs in a circuit for a signal.

First the signal varies normally during driving. The diagnostic trouble code test starts after some time (5), is then run cyclically in a pre-defined pattern and monitors the signal. Limit values for monitoring to consider the signal as incorrect is a voltage lower than 0.50 V (2) or higher than 4.85 V (1). An open circuit occurs in the circuit and the signal becomes 0 V (4). Monitoring detects this, waits so that the malfunction is confirmed and then stores a diagnostic trouble code (6).

Scheme 23

If the diagnostic trouble code test (5) starts after the malfunction (4) occurs, then monitoring will detect the malfunction fist when the test starts. Then monitoring waits so that the malfunction is confirmed and then stores a diagnostic trouble code (6). If you want the control module to detect a malfunction in the vehicle, you have to make sure that the control module's diagnostic trouble code test starts or is started.

HINT: If a malfunction occurs which has not yet been detected by the control module's monitoring, since the diagnostic trouble code test has not started, the vehicle may still exhibit a symptom.

Note. Conditions for diagnosis are described in the diagnostic trouble code information for every diagnostic trouble code.

Most diagnosis (at least non-emission-related diagnosis) are repeated periodically during the driving cycle, and every time they are repeated, a test is run that either results in a malfunction being detected or no malfunction being detected.

To enable the emission-related diagnosis to be completed and the diagnostic trouble code to be confirmed (with MIL-light activated as a result), several driving cycles in a row must be completed with a detected malfunction.

To enable the non-emission-related diagnosis to be completed (at least once), in principle the start conditions must be fulfilled for a certain time (from fractions of a second to a number of seconds).

Certain diagnoses require a completed driving cycle (e. g., ignition on, ignition off, and ignition on again) for the diagnosis to be considered as complete. Other diagnoses requires several other conditions to be fulfilled, e. g., with regards to

1. vehicle speed
2. engine coolant temperature (ECT)
3. time since start
4. different load and engine speed relationships in the same trip
5. a certain event (for example, that the component operates).

HINT: To assess if a test/diagnosis for the diagnostic trouble code is started or completed, status identifiers can be used. Turning off the ignition and then turning it on again often results in start of a new driving cycle/operation cycle, which results in update of status identifiers.

When, e. g., the engine control module (ECM) has run all diagnostics, the control module has completed a "trip". An extensive driving schedule in various conditions is required to complete a trip. The engine may also need to be shut off for a certain amount of time and then switched on again to complete a trip.

Emissions related diagnostic functions

Control modules that have and control emission-related components or functions, e. g., Engine control module (ECM) and Transmission control module (TCM), check that emission-related systems work. These systems are checked by running a diagnostic function. The diagnostic function checks the included components and that the function itself works in the system.

Lighting the malfunction indicator lamp (MIL)

In the event of emissions related diagnostic trouble codes (DTCs), a counter counts down to determine when to light the malfunction indicator lamp (MIL). The conditions for lighting the malfunction indicator lamp (MIL) vary depending on which diagnostic trouble code (DTC) is stored.

Note. If a malfunction becomes intermittent or the malfunction disappears, then the MIL-light turns off first after 3 driving cycles in a row are completed with malfunction detection.

Self-erasing of emission-related diagnostic trouble codes

After 40 driving cycles without detected malfunction with start of cool engine, where the engine temperature (coolant temperature) increases more than 5 °C (approx. 9 °F) and the final temperature is above approx. +71 °C (159.8 °F), then the diagnostic trouble code is erased. Diagnoses (diagnostic trouble code tests) for misfire and fuel adaptions require 80 driving cycles. These driving cycles are defined as a "warm-up cycle".

STATUS IDENTIFIER VOLVO DIAGNOSTICS II

The following identifiers are available (showed values apply until updated with a new read-out)

1. SB 01 Diagnostic trouble code test run in progress.
2. SB 02 Diagnostic trouble code test run at least once during current driving cycle.
3. SB 03 Sporadic/single malfunctions found the last time diagnostic trouble code test was run during current driving cycle/operation cycle.
4. SB 04 Sporadic/single malfunctions found at least once during current driving cycle.
5. SB 05 Request light warning light/text message due to detected malfunction.
6. SB 06 Diagnostic trouble code test blocked due to malfunction found by another diagnostic trouble code test.
7. SB 08 Malfunction detection counter, current value.
8. SB 09 Malfunction detection counter, maximum value reached some time during current operation cycle.

Abbreviation SB is from the English 'Status Bit'.

Scheme 24

The upper graph shows a varying signal value. If the signal value exceeds a max. value, which is considered a malfunction by the control module, then a sporadic malfunction is registered, that is, a malfunction is about to occur. Then the grey-marked surface indicates the signal considered to be incorrect.

The text below uses the term Driving cycle, which may also be called Operation cycle.

Note. If the diagnostic trouble codes are erased, the status identifiers are also erased

SB01 Diagnostic trouble code test run in progress (second paragraph from top).

Shows if the diagnostic trouble code test runs or not right now (in current driving cycle). It is only when the test runs that the control module can detect malfunctions and generate diagnostic trouble codes.

Grey-marked surface means that the test runs and can detect a malfunction if it occurs. The surface is "dashed", showing that when the diagnostic trouble codes runs, it runs in a cyclic, pre-determined pattern.

Status identifier 03 and 04 shows if a malfunction is detected or not. In this case, a malfunction is detected 3 times.

Status alternative when reading out is Yes (test runs now) or No (test is not run now).

SB02 Diagnostic trouble code test run at least once during current driving cycle (third graph from the top).

Shows if the diagnostic trouble code test has been run or not during the current driving cycle. If it has been possible for the control module to detect malfunctions and generate diagnostic trouble code any time during the current driving cycle.

Grey-marked surface means that the diagnostic trouble code test has been run at some time. If the diagnostic trouble code test has been run at some time in this driving cycle, status will always be Yes and remain so until the ignition is turned on off and a new driving cycle starts. When a new driving cycle starts, status identifiers are "reset" and is initially No.

Status identifier 03 and 04 shows if a malfunction is detected or not.

Status alternative when reading out is Yes (test completed) or No (test not completed).

SB03 Sporadic/single malfunctions found the last time diagnostic trouble code test was run during current driving cycle (fourth graph from the top).

A sporadic malfunction (intermittent malfunction) has been detected 3 times the last time the diagnostic trouble code test was run during current driving cycle. During the diagnostic trouble code test run the last time (status identifier 01) a malfunction has been detected 3 times.

Status alternative when reading out is Yes (sporadic malfunction found) or No (no sporadic malfunction found).

Note. When the control module detects the malfunction for the first time(status identifier 03 and 04), a diagnostic trouble code has not yet been stored. It is first when the malfunction detection counter 08 reaches a certain value that the control module considers that a real malfunction exists (a confirmed malfunction) and the diagnostic trouble code is stored.

SB 04 Sporadic/single malfunctions found at least once during current driving cycle (fifth graph from the top).

A sporadic malfunction (intermittent malfunction) has been detected at some time during current driving cycle. Grey. marked surface means that a malfunction has been detected at some time.

If the diagnostic trouble code test has been run at some time in this driving cycle, status will always be Yes and remain so until the ignition is turned on off and a new driving cycle starts. When a new driving cycle starts, status identifiers are "reset" and is initially No. Status identifier 03 and 04 shows if a malfunction is detected or not.

Status alternative when reading out is Yes (test has been run earlier) or No (test has not been run).

SB 05 Request light warning light/text message due to detected malfunction (sixth paragraph from the top).

Information that diagnostic trouble code activates a warning light or text message in driver information module. In this case, lighting of warning light is requested when the diagnostic trouble code has been confirmed and stored.

Status alternative when reading out is Yes (request performed) or No (no request).

SB06 Diagnostic trouble code test blocked (seventh graph from top).

Information that diagnostic trouble code test is turned off as a result of another malfunction and diagnostic trouble code is generated where the root cause is detected. If this in turn results in subsequent malfunctions, it prevents generation of subsequent diagnostic trouble codes. In this case, the diagnostic trouble code test is not blocked.

Status alternative when reading out is Yes (diagnostic trouble code test blocked) or No (diagnostic trouble code test not blocked).

SB08 Malfunction detection counter, current value (eight graph from top).

When a sporadic malfunction is detected by the control module the malfunction detection counter counts up as long as the malfunction exists.

When the malfunction no longer exists the counter counts down again. This is the basis for the control module's decision to store the diagnostic trouble code and the diagnostic trouble code is stored in the vehicle first when the counter reaches a certain max. value. This max. value varies between different diagnostic trouble codes.

Count rate of the counter is controlled as long as the malfunction exists before it causes customer symptom. The counter is used to decide if it is a real malfunction that has occurred and that has existed for some time. It is the control module's way of confirming the diagnostic trouble code, that is, confirming that a real malfunction exists.

SB09 Malfunction detection counter, max. value during current operation cycle

Shows max. value that status identifier 08 has reached during current driving cycle. When a new driving cycle starts, the counter is "reset".

STATUS IDENTIFIER GENERIC GLOBAL DIAGNOSTICS (GGD)

The following identifiers are available (showed values apply until updated with a new read-out)

1. SB 00 Malfunction found the last time that the diagnostic trouble code test was run during current driving cycle
2. SB 01 Malfunction found at least once during the current driving cycle
3. SB 02 Malfunction found at least once during the current and previous driving cycles
4. SB 03 Malfunction found recently since erasing of diagnostic trouble codes
5. SB 04 Diagnostic trouble code test run at least once since erasing of diagnostic trouble codes
6. SB 05 Malfunction found at least once since erasing of diagnostic trouble codes
7. SB 06 Diagnostic trouble code test run at least once during current operation cycle.
8. SB 07 Request light warning light/text message due to detected malfunction.

Scheme 25

The upper graph shows a varying signal value. If the signal value exceeds a max. value, which is considered a malfunction by the control module, then a sporadic malfunction is registered, that is, a malfunction is about to occur. Then the grey-marked surface indicates the signal considered to be incorrect.

The text below uses the term Driving cycle, which may also be called Operation cycle. The order of status identifiers in illustration and in the list below are presented as they belong to each other, not in numerical order.

Note. If the diagnostic trouble codes are restored, the status identifiers are also restored

Graph A Diagnostic trouble code test active

Shows if the control module's diagnostic trouble code test is active or not. The blue surface indicates when the test is active. The surface is "dashed", which shows when the diagnostic trouble code test runs it runs in a cyclically pre-determined pattern. Not included as a status identifier.

Graph B Malfunction active

Shows if the malfunction in the vehicle is active or not. The red surface indicates when the malfunction is present (active). Not included as a status identifier.

Graph C Counter 6 malfunction detection (C#6)

The counter counts the number of internal detections of the malfunction that have been performed for the diagnostic trouble code. Not included as a status identifier. When this counter reaches value +127 the control module considers the malfunction to be active right now.

When the counter is at value -128, the malfunction is not active. The value is reset for every new driving cycle.

If the value increases towards +127, the control module has detected a malfunction and for every internal test the value is counted up. When the malfunction no longer exists, the control module counts down to minimum -128.

The value on the control module can only be changed when it has started the test for the diagnostic trouble code. How big each step is that the control module counts up or down the value by to reach the limits +127 or -128 may vary between control modules. Limits +127 and -128 are pre-defined limits in the control module.

In the graph, the counter first counts down to -128 when the diagnostic trouble code test starts (graph A). When a malfunction occurs (graph B) and the diagnostic trouble code test detects the malfunction, first the counter's value is reset to 0, then it scrolls up to +127. Only then the malfunction is considered to exist. If the malfunction disappears and the diagnostic trouble code test is active, the counter counts down to -128.

SB 06 Diagnostic trouble code test run at least once during current operation cycle

Shows if the control module has performed diagnostic trouble code test for this diagnostic trouble code in current driving cycle. When the diagnostic trouble code test starts and counter 6 (malfunction detection) counts down to -128 (no malfunction found) or up to +127 (malfunction found), the control module considers that diagnostic trouble code test has been run.

Yellow-marked surface means that diagnostic trouble code test is not yet run.

Status alternative when reading out is Run or Not run.

SB 00 Malfunction found the last time that the diagnostic trouble code test was run during current driving cycle

Shows if the control module detects the malfunction right now. It is only when the test runs that the control module can detect malfunctions and generate diagnostic trouble codes. A malfunction has been detected 2 times during the current driving cycle. Note that only when counter 6 (malfunction detection) reaches the value +127 is it considered to be a malfunction. When the value gas dropped from +127 to 0, it is considered that there is no longer a malfunction.

Status alternative when reading out is Yes (malfunction detected right now) or No (no malfunction detected right now).

SB 01 Malfunction found at least once during the current driving cycle

Shows if the control module has detected the malfunction anytime during the current driving cycle. It is only when the test runs that the control module can detect malfunctions and generate diagnostic trouble codes. The diagnostic trouble code test has started and a malfunction has been detected at least 1 time during the current driving cycle.

Status alternative when reading out is Yes (malfunction found) or No (malfunction not found).

This status identifier is generated at the same time as status identifier SB00 and will remain in status Yes for the rest of the current driving cycle. At start of a new driving cycle, it has changed to status No until a malfunction is detected again.

SB 05 Malfunction found at least once since erasing of diagnostic trouble codes

Shows if the control module has detected the malfunction during earlier driving cycle. A malfunction has been detected at least 1 time since the diagnostic trouble code was erased the last time.

Status alternative when reading out is Yes (malfunction found) or No (malfunction not found).

This status identifier is generated at the same time as status identifier SB 00 and will remain in status Yes until diagnostic trouble codes are erased once again.

SB 04 Diagnostic trouble code test run at least once since erasing of diagnostic trouble codes

Shows if the control module has performed diagnostic trouble code test for this diagnostic trouble code in current and/or earlier driving cycle since the diagnostic trouble code was erased the last time. This means that if diagnostic trouble code test has been run after erasing of diagnostic trouble codes, it will remain in Run until diagnostic trouble codes are erased once again.

Yellow-marked surface means that diagnostic trouble code test has been run.

Status alternative when reading out is Run or Not run.

This status identifier is generated at the same time as status identifier SB 06.

SB 07 Request for lit warning light/text message

Information about the diagnostic trouble code activates a warning light or text message. In this case, lighting of the warning light is requested when a diagnostic trouble code is stored.

Status alternative when reading out is Yes (request performed) or No (no request).

SB 02 Malfunction found at least once during the current and previous driving cycles

Pending not yet confirmed diagnostic trouble code.

Status alternative when reading out is Yes (malfunction found but not confirmed) or No (no malfunction found).

This status identifier is generated at the same time as status identifier SB 00 is generated for the first time and will remain in status Yes until certain driving cycle conditions are fulfilled and no malfunctions are detected. After a certain number of driving cycles without detected malfunction, it returns to status No. Number of driving cycles required depends on the system.

SB 03 Malfunction found recently since erasing of diagnostic trouble codes

Confirmed diagnostic trouble code.

Status alternative when reading out is Yes (malfunction found and confirmed) or No (no malfunction found).

This status identifier is generated at the same time as status identifier SB 00 is generated for the first time and will remain in status Yes until certain driving cycle conditions are fulfilled and no malfunctions are detected. After a certain number of driving cycles without detected malfunction, it returns to status No. That is, if a malfunction becomes intermittent and no longer is detected, the status will change to No. Number of driving cycles required depends on the system.

Note. For emission-related control system, this status identifier is generated to status Yes (Malfunction found and confirmed), first after status identifier SB02 has had status Yes (Malfunction found but not confirmed) for 2 driving cycles in a row with malfunction detected.

PRACTICAL USE OF DIAGNOSTICS

GENERAL

There are several ways to decide if the malfunction is active right now or not as well as when the malfunction occurred

1. Read off the diagnostic trouble code's counter, status identifier and frozen values. By interpreting these you can find out when the malfunction was stored, how often the malfunction has occurred (intermittence) and what the driving conditions were when the malfunction was stored.
2. Read off a parameter for component/system and decide if the value is correct or not. By, e. g., manually affecting the sensor or the switch, you can decide immediately if the parameter (signal) with its circuit is correct.
3. Trigger a component (activate) and decide if the component/function is affected or not. By triggering, e. g., the relay and listening for its clicking sound or the function which is to be affected, it is possible to decide immediately if the component is correct.
4. Decide if the vehicle shows any symptom (malfunction). If the vehicle no longer shows the symptom, one may suspect that the malfunction no longer is active.

The following accounts in detail for some of the above.

TO DECIDE DIAGNOSTIC TROUBLE CODE TEST'S STATUS

By reading out the diagnostic trouble code with associated status identifier, then status for the diagnostic trouble code test that detects the malfunction and generates the diagnostic trouble code, is obtained.

Example 1, Permanent malfunction

Status identifier

The diagnostic trouble code test has been run in both current driving cycle and in earlier driving cycles. Malfunction has been detected both in current driving cycle and in previous driving cycle, which indicates that the malfunction is active right now. The control module has requested lighting of the warning light.

Conclusion: Permanent malfunction.

Assessment: Very good chance to repeat the customer symptom and thus succeed with troubleshooting, as the malfunction has been found in current and in previous driving cycle. Since the malfunction has been detected during the present run cycle, it does not really matter for troubleshooting if the malfunction has been detected in all previous driving cycles or not. If this information is supplemented with the counters' values you can decide how "permanent" the malfunction is.

If the vehicle is stationary, e. g., with the ignition on, this means that the test runs directly when the ignition is turned on. This makes it easier to both fins the malfunction and to verify that the malfunction cause has been take care of.

Example 2, Unknown status

Status identifier

The diagnostic trouble code test has been run in previous run cycles but not in current driving cycle. Malfunction has been detected in previous run cycle, but not in current driving cycle since the test has not started. Warning light is on.

Conclusion: Unknown status

Assessment: Since the test has not started in the current driving cycle it is not possible to decide if the malfunction is "active" right now. First read the diagnostic trouble code information and try to obtain conditions so that the test is started and run, which enables detection of the malfunction. If the malfunction is detected, chances are very good to repeat the customer symptom, and thus succeed with troubleshooting as the malfunction has been found in the current driving cycle.

If the malfunction was not detected even though conditions are fulfilled, then chances are less good to repeat the customer symptom, and thus succeed with troubleshooting as the malfunction has not been found in the current driving cycle.

DIAGNOSTIC FUNCTIONS

GENERAL

The control module has a built-in diagnostic system, Volvo Diagnostic, which continuously monitors internal functions as well as input and output signals.

A diagnostic trouble code (DTC) is stored if the control module detects a fault. Should a fault disappear for any reason after being permanently stored in the control module as a diagnostic trouble code (DTC), the information remains stored in the control module.

Stored diagnostic trouble codes (DTCs) can be read off and erased using this function.

Diagnostic trouble codes (DTCs) can only be erased once all the diagnostic trouble codes (DTCs) have been read off at least once.

see DIAGNOSTIC FUNCTIONS

GENERAL

The control module has an integrated diagnostic system, which continuously monitors its own system as well as the input and output signals.

DIAGNOSTIC TROUBLE CODES (DTC)

If the control module detects a fault then it stores a diagnostic trouble code (DTC). If a fault disappears for any reason after a diagnostic trouble code (DTC) has been permanently stored in the control module then the information on the diagnostic trouble code (DTC) remains in the control module.

READING AND ERASING DIAGNOSTIC TROUBLE CODES (DTC)

Stored diagnostic trouble codes (DTC) can be read off and erased using this function.

Note. Diagnostic trouble codes (DTC) can be erased even if all diagnostic trouble codes (DTC) have not been read off at least once.

GENERAL

The control module has an integrated diagnostic system, which continuously monitors its own system as well as the input and output signals.

If the control module detects a fault then it stores a diagnostic trouble code. If a fault disappears for any reason after a diagnostic trouble code has been permanently stored in the control module then the information on the diagnostic trouble code remains in the control module in a number of driving cycles that can be calibrated.

Stored diagnostic trouble codes (DTCs) can be read off and erased using this function.

Note. Diagnostic trouble codes (DTCs) can be erased without having been read off.

DIAGNOSTIC FUNCTIONS, PASSENGER DOOR MODULE (PDM)

GENERAL

The control module has a built-in diagnostic system, Volvo Diagnostic, which continuously monitors internal functions as well as input and output signals.

A diagnostic trouble code (DTC) is stored if the control module detects a fault. The passenger door module can store up to 10 diagnostic trouble codes (DTCs).

Should a fault disappear for any reason after being permanently stored in the control module as a diagnostic trouble code (DTC), the information remains stored in the control module.

Diagnostic trouble codes (DTCs) can only be erased once all the diagnostic trouble codes (DTCs) have been read off at least once.

DIAGNOSTIC FUNCTIONS, DRIVER'S DOOR MODULE (DDM)

GENERAL

The control module has a built-in diagnostic system, Volvo Diagnostic, which continuously monitors internal functions as well as input and output signals.

The control module will store a diagnostic trouble code (DTC) if it detects a fault. The driver's door module can store up to 10 diagnostic trouble codes (DTCs).

Should a fault disappear for any reason after being permanently stored in the control module as a diagnostic trouble code (DTC), the information remains stored in the control module.

Diagnostic trouble codes (DTCs) can only be erased once all the diagnostic trouble codes (DTCs) have been read off at least once.

LEAK DIAGNOSTICS, ORIGINAL VERSION

To minimize false detection of leakage, new software has been released for the Engine control module (ECM). The software has been released afterwards, in order of priority, started at the end of 2006.

The improved software version makes diagnostics more robust and durable against aging and wear of the leak diagnostic unit. It affects strategies, behavior and to a degree also read off parameters.

All gases that evaporate from fuel in the fuel tank must be led to and stored in the evaporative emission system (EVAP) canister so that they can be directed into the engine for combustion. In order to detect leakages which cause evaporation of gases into the air, the fuel tank system is diagnosed for leakage. The fuel tank system consists of

1. fuel tank
2. Canister purge (CP) valve (1)
3. EVAP canister (2)
4. leak diagnostic unit (3)
5. air cleaner (ACL) (4)
6. Roll-over valve (5)
7. Float Limit Vent Valve (6)
8. fuel filler pipe (7)
9. all lines between the above components.

The fuel tank system has a leak diagnostic unit to diagnose any leakage. The leak diagnostic unit pressurizes the fuel tank system when the ignition is off, if the conditions for diagnosis have been met. The control module can detect faults in the function of the leak diagnostic unit and leakage that is 0.5 mm or greater. Minor leak; leakage greater than 0.5 mm but less than 1.0 mm. Major leak; leakage greater than 1.0 mm.

The leak diagnostic unit consists of a pump and a valve that controls the air flow in the unit. The fuel tank system tests for leaks by measuring the power consumption of the pump. The power consumption of the pump corresponds to a certain pressure in the fuel tank system. During diagnosis, the rate at which the pressure can build up is checked, taking into account the quantity of fuel in the tank. The quicker the pressurization the better the fuel tank system is sealed.

Conditions for diagnosis

The diagnosis begins when all the following conditions are met

1. There must be no diagnostic trouble code (DTC) stored for the following components or functions: the power stage for the pump in the leak diagnostic unit the power stage for the valve in the leak diagnostic unit the power stage for the EVAP canister purge valve the EVAP canister purge valve. the engine coolant temperature (ECT) sensor atmospheric pressure sensor outside temperature sensor.
2. The engine is switched off until the engine coolant temperature (ECT) has fallen to a few degrees above the outside temperature, then engine running for at least 10 minutes.
3. Ignition off
4. Vehicle speed 0 km/h
5. Engine coolant temperature (ECT) -5°C or higher.
6. Maximum altitude of 2500 meters above sea level.
7. Outside temperature between -5 and +35°C.
8. Fuel volume in the tank less than 85%. The engine control module (ECM) ignores these parameters if a diagnostic trouble code (DTC) is stored for the fuel level sensor and the fuel volume cannot be determined.
9. Battery voltage between 11.0-15.0 V. The voltage must be stable.
10. EVAP canister purge valve closed
11. Low volume in the canister.
12. Fuel tank filler cap locked. Tip. Locking occurs when the vehicle speed exceeds approximately 20 km/h.

Diagnostic phases

The diagnostic is divided into the following phases and is carried out in sequence when all conditions for the diagnostic have been met.

1. reference phase
2. function test
3. leak diagnostic

Reference phase (1-2)

The illustration is a diagram of a fault free fuel tank system.

Before the leak diagnostic begins, the control module runs a reference phase for leakage. During the reference phase (1-2) for leakage that is 0.5 mm, the pump in the leak diagnostic unit pumps ambient air through a 0.5 mm hole and back out to the ambient air. At the same time, the power consumption (A) of the pump is measured and stored in the control module. The stored value (A) for the power consumption of the pump corresponds to a leakage of 0.5 mm. This value is then used by the engine control module (ECM) to determine the leak status of the fuel tank system.

Function test (1-3)

If the value for the power consumption of the pump is too high or low during reference phase (1-2), or if the value for pump power consumption varies too much during reference phase (1-2), the diagnostic is cancelled and starts again the next time the conditions for the diagnostic are met. A diagnostic trouble code (DTC) is stored if the diagnostic is cancelled because the power consumption of the pump is varying excessively.

After the reference phase, the valve (2) in the leak diagnostic unit is activated and controls the air flow to the fuel tank to pressurize the fuel tank system. This change of air flow will cause the power consumption of the pump to fall briefly before the pressure builds up in the fuel tank system (3). A diagnostic trouble code is stored if the value for the power consumption of the pump drops too quickly, slowly or not at all.

Leak diagnostic, major leak (leakage greater than 1.0 mm)

The diagnostic for "major leaks" is carried out each time when the conditions for the diagnostic are met. The leak diagnostic unit pressurizes the fuel tank system, measures the power consumption of the pump (4) and compares this with a calculated desired value (B). A diagnostic trouble code (DTC) for a major leak is stored if the measured value does not reach the calculated desired value within a certain time (the time is determined by atmospheric pressure and the fuel level in the tank).

Leak diagnostic, minor leak (leakage greater than 0.5 mm but less than 1.0 mm)

The diagnostic for minor leaks is run every other time that the conditions for the diagnostic are met. The diagnostic for major leaks is always run before the diagnostic for minor leaks. The leak diagnostic unit continues to pressurize the fuel tank system (5-6). After a certain amount of time (the time varies depending on the fuel level in the tank), the engine control module (ECM) checks that the fuel tank system for leaks. This is determined based on

1. time
2. the measured reference current consumption of the pump (A)
3. the measured power consumption of the pump when the assessment is made
4. the shape and character of the current curve during pressurization.

A diagnostic trouble code (DTC) is stored if a minor leak is detected.

LEAK DIAGNOSTICS, IMPROVED VERSION

All gases that evaporate from fuel in the fuel tank must be led to and stored in the evaporative emission system (EVAP) canister so that they can be directed into the engine for combustion. In order to detect leakages which cause evaporation of gases into the air, the fuel tank system is diagnosed for leakage. The fuel tank system consists of

1. fuel tank
2. Canister purge (CP) valve (1)
3. EVAP canister (2)
4. leak diagnostic unit (3)
5. air cleaner (ACL) (4)
6. Roll-over valve (5)
7. Float Limit Vent Valve (6)
8. fuel filler pipe (7)
9. all lines between the above components.

The fuel tank system has a leak diagnostic unit to diagnose any leakage. The leak diagnostic unit pressurizes the fuel tank system when the conditions for diagnosis have been met. The control module can detect faults in the function of the leak diagnostic unit and leakage that is 0.5 mm or greater. Minor leak; leakage greater than 0.5 mm but less than 1.0 mm. Major leak; leakage greater than 1.0 mm.

The leakage diagnostic consists of a pump and a valve that control the flow in the unit. Engine control module (ECM) checks sealing in the tank system by measuring the relationship between obtained pressure and flow from the leakage diagnostic pump when pressurized.

If a certain pressure is not obtained with a pre-determined (with known mass) the Engine control module (ECM) interprets it as a leakage from the fuel tank system.

Leakage diagnostics start in normal operation when specific conditions have been fulfilled, see below. Diagnostics can also be started by command using VIDA when you disregard some of these conditions.

Conditions for diagnosis

The diagnosis begins when all the following conditions are met

Note. Slightly different conditions apply when diagnostics are started by command using VIDA (Volvo scan tool).

1. No diagnostic trouble codes for EVAP-valve or atmospheric pressure sensor may be stored.
2. The engine is switched off until the engine coolant temperature (ECT) has fallen to a few degrees above the outside temperature, then engine running for at least 10 minutes.
3. Ignition off
4. Vehicle speed 0 km/h
5. Engine temperature 4-35 °C.
6. Maximum altitude of 2500 meters above sea level.
7. Outdoor temperature between 4-35 °C.
8. Fuel volume in the tank between 0-85%. The engine control module (ECM) ignores these parameters if a diagnostic trouble code (DTC) is stored for the fuel level sensor and the fuel volume cannot be determined.
9. Battery voltage between 11-15 V. The voltage must be stable.
10. EVAP canister purge valve closed
11. Low volume in the canister.
12. Tank hatch locked. NOTE: Locking occurs when the vehicle speed exceeds 20 km/h.

Diagnostic phases

The diagnostic is divided into the following phases and is carried out in sequence when all conditions for the diagnostic have been met.

1. reference phase
2. function test
3. checking tank system.

Reference phase

Before leakage diagnosis itself can be started, the control module performs a reference phase for leakage. Reference phase for leakage which is 0.5 mm is performed by the leakage diagnostic unit's pump pumping ambient air through a hole which is 0.5 mm and back out to the ambient air. During that time, the pump is monitored n the leakage diagnostic unit and reference values are stored away for later use in assessing the tank system's sealing.

If any reference value for the pump is unreasonably high or low, or varies too much, then diagnosis is interrupted and a diagnostic trouble code is generated.

Function test

After the reference phase, the leakage diagnostic unit's valve is activated and the air flow is controlled to the tank system to pressurize the tank system. This shift in air flow means that the pump load drops briefly before the pressure builds up in the tank system. If the load does not change within reasonable limits within reasonable time, then diagnosis is interrupted and a diagnostic trouble code is generated.

Checking tank system, major leakage (leakage bigger than 1.0 mm)

Diagnosis are performed every time conditions for diagnosis are fulfilled.

The leakage diagnostic unit pressurizes the tank system and checks sealing by monitoring the pressure in the tank system. The pressure is a calculated pressure, calculated using measured power consumption on the pump. If the pressure stabilizes and/or does not go above 1500 Pa within 450 seconds, this is interpreted as a leakage from the fuel tank system. Diagnosis is interrupted and a diagnostic trouble code for major leakage is generated.

Checking tank system, minor leakage (leakage bigger than 0.5 mm but smaller than 1.0 mm)

Diagnosis for minor leakage is performed every other time conditions for diagnosis are fulfilled. Otherwise, diagnosis finishes after checking for major leakage.

The leakage diagnosis unit continues pressurizing the tank system. Engine control module (ECM) checks sealing in the tank system by measuring the relationship between reached pressure and flow from the leakage diagnosis pump when pressurizing. In a sealed system the relationship between these shall be linear. Any deviations from the linear relationship is calculated and used to assess the tank system's sealing.

If the assessment, performed within 15 minutes, is that a minor leakage has been detected in the tank system, a diagnostic trouble code for minor leakage is generated.

see DIAGNOSTIC FUNCTIONS

MISFIRE DIAGNOSTIC

See: MISFIRE DIAGNOSTIC

CAMSHAFT DIAGNOSTICS (CVVT)

See: CAMSHAFT DIAGNOSTICS (CVVT)

LEAK DIAGNOSTICS (CERTAIN MARKETS ONLY)

See: LEAK DIAGNOSTICS (CERTAIN MARKETS ONLY)

HEATED OXYGEN SENSOR (HO2S) DIAGNOSTIC

See: HEATED OXYGEN SENSOR (HO2S) DIAGNOSTIC

THREE-WAY CATALYTIC CONVERTER (TWC) DIAGNOSTICS

See: THREE-WAY CATALYTIC CONVERTER (TWC) DIAGNOSTICS

FUEL PRESSURE REGULATION, DIAGNOSTICS

See: FUEL PRESSURE REGULATION, DIAGNOSTICS

CONDITIONS FOR DIAGNOSIS

For the diagnosis of a component or function to start, certain specific conditions must be met. The conditions for diagnostics vary depending on the component or function being diagnosed.

Conditions must be met during the diagnostic in order for the diagnostic to be completed. The time and conditions for the diagnostic vary depending on the component or function being diagnosed. Certain diagnostics only require the ignition to be switched on and off for a diagnostic to be run. Other diagnostics require that several different conditions are met. For example

1. vehicle speed
2. engine coolant temperature (ECT)
3. time since start
4. different load and engine speed relationships in the same trip
5. a certain event (for example the evaporative emission system (EVAP) valve is operating).

When the engine control module (ECM) has run all the implemented diagnostics, the control module has completed a "trip". An extensive driving schedule in various conditions is required to complete a trip. The engine may also need to be shut off for a certain amount of time and then switched on again to complete a trip.

EMISSION-RELATED DIAGNOSTIC FUNCTIONS

The engine control module (ECM) checks that the emission-related systems are working. These systems are checked by running a diagnostic function. The diagnostic function checks the components and that the system is functioning.

DIAGNOSTIC TROUBLE CODE MEMORY

When the engine control module (ECM) detects a fault, the diagnostic trouble code (DTC) and status are stored in the diagnostic trouble code (DTC) memory and are now visible at normal diagnostic trouble code (DTC) read out. If the diagnostic trouble code (DTC) lights the malfunction indicator lamp (MIL) this occurs at the same time. If an existing fault disappears and does not recur, the engine control module, after a certain number of fault-free operating cycles and depending on the DTC, changes the status of the diagnostic trouble code (DTC). This means that it can no longer be read off at normal DTC read out. In this status, the diagnostic trouble code (DTC) remains until the engine control module (ECM) erases diagnostic trouble code (DTC) or is disconnected from power.