25-pin data link connector diagnostics

You will require a PicoScope to perform this test. A list of suitable accessories can be found at the bottom of this page.

How to perform the test

Please note that this sequence is based on the 25-pin DLC fitted to Mazda variants as listed in the Fault Code Table.

  1. Plug one BNC test lead into Channel A of the oscilloscope.
  2. Connect a Back-pinning Probe to the colored plug on the BNC test lead, and probe it into the 'B+' terminal on the DLC socket.
  3. Connect another Back-pinning Probe to the black plug on the BNC test lead and probe it into the 'FEN' terminal on the DLC Socket as shown in Figure 1.
  4. Using a suitable piece of insulated wire, connect one end to the DLC socket into the 'TEN' terminal and connect the other end to the 'GND' terminal.
  5. Press the spacebar on the PC to start the scope displaying live data.
  6. Switch on the vehicle ignition and follow the instructions below. The codes will then appear on the screen, as shown below.

Accessing fault codes from the PCM memory

Once the scope has been correctly connected to the 25-pin DLC socket:

  1. Switch the ignition on.
  2. The codes will now be displayed on the screen. Once the first code is repeated, this indicates all codes have been read from the PCM.
  3. Switch ignition off.
  4. Analyze any codes retrieved from PCM.

Erasing fault codes from the PCM memory

  1. Ensure the ignition is switched off.
  2. Disconnect the battery earth cable for at least 30 seconds.
  3. Depress the brake pedal for at least 20 seconds (total 50 seconds).
  4. Reconnect the battery earth cable.
  5. Repeat the code reading sequence to ensure all DTCs have been removed from the memory of the PCM.

WARNING: Disconnecting the battery may erase the memory from ancillary devices such as clocks and radios.

Important Note: This sequence is for the Mazda variants listed in the Fault Code Table. For other manufacturers, check if the vehicle is equipped with a 25-pin DLC connector and also check to see if the above test can be carried out. Serious damage to the PCM will occur if the test is carried out on a vehicle that does not support the above test method. Refer to the manufacturer's wiring and technical information for further support.

Waveform notes

How to interpret the codes from the example waveforms

The sequence begins with a long pulse, indicating the start of the code-reading sequence from the PCM. The example waveforms show codes in the 4-digit EOBD/OBDII format, but other variants of Mazda give a two-digit code flash sequence. Consult the manufacturer's technical information for two-digit codes.

The 4-digit code in Code Sequence 1 is indicated by 4 groups of signals.

Digit 1

  • The first digit is a single, long pulse (indicated by a white arrow)
  • As there is no short pulse, the first digit is a 0.

Digit 2

  • Digit 2 consists of a long pulse (white arrow) followed by a short pulse (black arrow).
  • This pattern indicates that the second digit is a 1.

Digit 3

  • Digit 3 is again just a single long pulse, indicated by a white arrow.
  • This pattern indicates another 0.

Digit 4

  • Digit 4 is also a single long pulse (indicated by another white arrow).
  • This digit is another 0.

Putting these four digits together gives Code 0100, which is the EOBD Code for "Mass Air Flow (MAF) sensor/volume air flow (VAF) sensor circuit malfunction".

Example waveform 1

There are no pulses after the start pulse, indicating that all digits are 0. The table below tells us that:

Code P0000 = EOBD Code for No Fault Found.

Therefore there are no fault codes present on the vehicle.

Example waveform 2

There is one code that is repeated as it is the only code stored in the PCM. The table below tells us that:

Code P0110 = EOBD Code for Intake Air Temperature (IAT) Sensor.

Example waveform 3

The PCM is signalling 3 codes. The table below tells us that:

Code P0100 = EOBD Code for Mass Air Flow (MAF) sensor/volume air flow (VAF) sensor circuit malfunction.

Code P0110 = EOBD Code for Intake Air Temperature (IAT) Sensor.

Code P0120 = EOBD Code for Thottle Position (TP) sensor A/Accelerator pedal position (APP) sensor A circuit malfunction.

Notes

  • A long pulse followed by 2 short pulses indicates a '2', as shown in example waveform 3. Higher digits are obtained by adding more short pulses.
  • Each 4-digit code is separated from the next by an 8-second delay to allow you to tell them apart.
  • If only one code is stored in the PCM, then this code will be continuously repeated as a single fault code.
  • If more than one code is stored in the PCM, all codes will be read and then repeated untill the sequence is stopped.

Technical information

The engine management system is constantly monitored by the PCM as the engine is running under different loads and conditions. All of the input and the output signals are monitored at all times. This is done so that the PCM can keep control of the engine and maintain optimum running conditions at all times. The PCM checks the values from the sensors and compares them with the information stored in the ROM (Read Only Memory) of the PCM. Based on the information stored, the PCM changes the commands to the actuators to alter any parameters to keep optimum running.

While the PCM is reading from ROM and reading all the signals from the sensors and actuators, thus monitoring the operating parameters of the engine, it is also monitoring the tolerances and ranges of each sensor and actuator to see if they are working correctly. When the PCM sees that a component or tolerance is breached then it will initiate a DTC (Diagnostic Trouble Code) which is stored in the RAM section of the PCM, often known as KAM (Keep Alive Memory), or in the EEPROM (Electronically Eraseable Programmable Read Only Memory). The DTC is then stored until action is taken: the fault is rectified on a self-check system, or an instruction is sent to the PCM to clear the DTC and the system is rechecked to ensure that it is operating correctly again.

There are a number of different methods for accessing fault codes depending on the system used on the vehicle - EOBD, OBD I or OBD II:

  • Using the MIL Light on the Dashboard to flash the code in a given sequence.
  • Connecting a LED, test lamp or scope to a DLC connector and observing the long and short flashes (pulses).
  • Connecting a scan tool to the DLC connector and communicating with the PCM directly.

OBD-I (On-Board Diagnostics I)

This legislation requires that vehicles manufactured from 1988 onwards be equipped with a system that is controlled electronically by a computer and is capable of monitoring itself during operation. Any malfunction in the system that leads to an effect in the exhaust emissions has to illuminate a warning light on the dashboard and present a stored DTC. The DTC must accessible and readable with the use of on-board facilities such as Flash Code, LED, Test Lamp, Oscilloscope.

OBD-II

The legislation that supports OBD-II applies to vehicles that are manufactured from 1994 onwards (Spark Ignition Engines) and 1996 onwards (Compression Ignition Engines). The main features fitted and that have to be monitored constantly are as follows:

  • Internal Combustion
  • Catalytic Converter
  • Levels of Oxygen (Oxygen Sensors)
  • Secondary Air System
  • Fuel Evaporative Control
  • EGR (Exhaust Gas Recirculation)

The key features for DTCs are as follows:

  1. The Malfunction Indicator Lamp (MIL) has to be provided for warning the driver that a fault is present with an additional flashing function.
  2. The DTCs must be read from the PCM using a scan tool through the 16-Pin DLC Connector
  3. All emission-related components have to be monitored by the PCM for the operation of the engine as well as monitoring the components for defects.
  4. When a fault occurs, the system has to be capable of logging perfomance data in the form of a freeze frame.
  5. The codes must be formatted to a universal format so that all scan tools and diagnostic equipment can read them and the user can easily interpret them. See Figure 5.
CODE PART POSSIBLE ARRANGEMENT MEANING
1 B BODY Control Code
1 C CHASSIS Control Code
1 P POWERTRAIN Control Code OBD II
1 U UNDEFINED - Used for Network Systems, CAN Bus
2 0 Fault Code given under the SAE testing guidelines
2 1 Fault Code given under the Manufacturer's guidelines
2 2 Fault Code given under the Manufacturer's guidelines
2 3 Reverse Fault Code
3 1 Fuel and Air Measurement System
3 2 Fuel and Air Measurement System
3 3 Ignition System
3 4 Exhaust Control System
3 5 Engine Speed and Idling Control System
3 6 PCM, Computer Control & Output Signals
3 7 Transmission Control Systems
4 01 to 99 Assignment of System Components

Figure 5 - Structure of Standard Fault Codes

Additional information

The Fault Code Table below is specific to the vehicles listed.

FAULT CODE TABLE - MAZDA VARIANTS
Model: 323 (BG) - 323 ESTATE 1.6/4X4 (BW) - 323 (BA) - 323 1.3/1.5/1.8 (BJ) - 323 2.0 D/TD (BJ) - 626/MX-6 (GE) - 626/ESTATE 1.8/2.0 (GF/GW) - 626/ESTATE 2.0 TD (GF/GW) - XEDOS 6/9 - MX-3/MX-5
Year: 1989 - 2003
Engine Code: BP, BP-DOHC, B3, B3E, B6-SOHC, B6-DOHC, B6E, FP, FS, KF, KJ, KL, K8, RF, RF-CX, FR-TURBO, ZL, Z5
System: MAZDA EGI - MAZDA EDC
EOBD CODE LOCATION OF FAULT POSSIBLE CAUSE OF FAULT
P0 Refer to EOBD Diagnostic Trouble Codes. -
P2 Refer to EOBD Diagnostic Trouble Codes. -
U0 Refer to EOBD Diagnostic Trouble Codes. -
P1100 Mass Air Flow (MAF) Sensor - Circuit Intermittent Wiring, MAF Sensor
P1101 Mass Air Flow (MAF) Sensor - Circuit Intermittent Wiring, MAF Sensor
P1110 Intake Air Temperature (IAT) Sensor 2 Wiring, IAT Sensor
P1112 Intake Air Temperature (IAT) Sensor 2 - Circuit Intermittent Wiring, IAT Sensor
P1113 Intake Air Temperature (IAT) Sensor 2 Wiring, IAT Sensor
P1117 Engine Coolant Temperature (ECT) Sensor - Circuit Malfunction Wiring, ECT Sensor
P1120 Throttle Position (TP) Sensor - Low Input Wiring short to Earth, TP Sensor
P1125 Throttle Position (TP) Sensor - Circuit Intermittent Wiring, TP Sensor
P1130 Fuel trim (FT) - Control limit exceeded Intake/Exhaust leak, fuel pressure/pump, EVAP/EGR system, wiring, HO2S
P1131 Heated Oxygen Sensor (HO2S) - Low Voltage Intake/Exhaust leak, fuel pressure low, hose connection, HO2S/wiring short to earth, Injector(s), MAF Sensor/Wiring
P1132 Heated Oxygen Sensor (HO2S) - High Voltage Intake/Exhaust leak, fuel pressure low, hose connection, HO2S/wiring short to positive, Injector(s), MAF Sensor/Wiring
P1170 Oxygen Sensor (O2S)/Heated Oxygen Sensor (HO2S), bank 1 - incorrect signal. Intake leak, fuel pressure/pump, wiring, O2S/HO2S, Injector(s), ECT Sensor, MAF Sensor, Spark Plugs
P1173 Oxygen Sensor (O2S)/Heated Oxygen Sensor (HO2S), bank 2 - incorrect signal. Intake leak, fuel pressure/pump, wiring, O2S/HO2S, Injector(s), ECT Sensor, MAF Sensor, Spark Plugs
P1182 Fuel Shut-Off Solenoid Wiring, Fuel Shut-Off Solenoid
P1189 Fuel Injection pump position/speed sensor Wiring, Fuel injection pump speed sensor
P1190 Module Coding Plug Wiring, Module Coding Plug
P1195 Barometric Pressure (BARO) Sensor Wiring, BARO Sensor, PCM
P1196 Ignition Switch, Start Signal - Circuit Malfunction Wiring, Starter Motor
P1221 Traction Control (TCS) System - Malfunction Wiring, TCS Malfunction
P1226 Fuel Quantity Adjuster Position Sensor - Circuit Malfunction Wiring, Fuel quantity adjuster position sensor
P1250 Fuel Pressure Regulator Control Solenoid Wiring, Fuel pressure regulator control solenoid
P1252 Fuel Pressure Regulator Control Solenoid 2 Wiring, Fuel pressure regulator control solenoid
P1279 Fuel Quantity Adjuster Position Sensor - Range/ Performance Problem Wiring, Fuel quantity adjuster position sensor
P1298 Fuel Quantity Adjuster Control Module - Circuit Malfunction Wiring, Fuel quantity adjuster control module
P1312 Fuel Injection Timing Valve Wiring, Fuel injection timing valve
P1318 Fuel Injection Timing Valve Position Sensor - Circuit Malfunction Wiring, Fuel injection timing valve position sensor
P1319 Fuel Injection Timing Valve Position Sensor - Range/Performance Problem Wiring, Fuel injection timing valve position sensor
P1345 Camshaft Position (CMP) Sensor - No Signal Wiring, Sensor Supply Voltage, CMP Sensor
P1402 Exhaust Gas Recirculation (EGR) Valve Position Sensor Wiring, EGR Valve position sensor
P1409 Exhaust Gas Recirculation (EGR) Valve - Circuit Malfunction Wiring, EGR Valve
P1474 Engine Coolant Blower Motor Relay - Circuit Malfunction Wiring, Engine Coolant Blower Motor Relay
P1485 Exhaust Gas Recirculation (EGR) Solenoid - Vacuum Wiring, EGR Solenoid
P1486 Exhaust Gas Recirculation (EGR) Solenoid - Vent Wiring, EGR Solenoid
P1487 Manifold Absolute Pressure (MAP) Sensor Solenoid Wiring, MAP Sensor Solenoid
P1496 Exhaust Gas Recirculation (EGR) Valve, Motor Coil 1 Wiring, EGR Valve
P1497 Exhaust Gas Recirculation (EGR) Valve, Motor Coil 2 Wiring, EGR Valve
P1498 Exhaust Gas Recirculation (EGR) Valve, Motor Coil 3 Wiring, EGR Valve
P1499 Exhaust Gas Recirculation (EGR) Valve, Motor Coil 4 Wiring, EGR Valve
P1500 Vehicle Speed Sensor (VSS) - Intermittent Signal Wiring, VSS
P1504 Idle Air Control (IAC) Valve Wiring, IAC Valve
P1508 Bypass Solenoid 1 Wiring, Bypass Solenoid
P1509 Bypass Solenoid 2 Wiring, Bypass Solenoid
P1521 Intake Manifold Air Control Solenoid 1 Wiring, Intake Manifold Air Control Solenoid
P1522 Intake Manifold Air Control Solenoid 2 Wiring, Intake Manifold Air Control Solenoid
P1523 Intake Manifold Air Control Solenoid 1 Wiring, Intake Manifold Air Control Solenoid
P1524 Intercooler Bypass Solenoid Wiring, Intercooler Bypass Solenoid
P1525 Air Bypass Valve Solenoid - Vacuum Wiring, Air Bypass Valve Solenoid
P1526 Air Bypass Valve Solenoid - Vent Wiring, Air Bypass Valve Solenoid
P1540 Air Bypass Valve Control Hose leak/blockage, Wiring, Air Bypass Valve Actuator/Solenoid
P1562 Engine Control Module (PCM) - Supply Voltage Low Battery, Alternator, Wiring
P1601 Data BUS, TCM Wiring, PCM, TCM
P1602 Engine Control Module (PCM)/Immobilizer Control Module - Communication Error Wiring, Reader Coil, Ignition Key, Immobilizer Control Module, ECM
P1603 Ignition Key - Not Programmed to PCM PCM Incorrectly/Not Programmed
P1604 Engine Control Module (PCM) / Immobilizer Code Not Stored PCM Incorrectly/Not Programmed
P1606 Engine Control Relay Wiring, Engine Control Relay
P1608 Engine Control Module (PCM) PCM
P1609 Engine Control Module (PCM) Knock Control PCM
P1621 Engine Control Module (PCM) / Immobilizer Control Module - Immobilizer Codes do not Match Incorrectly Programmed Immobilizer Control Module/PCM
P1622 Engine Control Module (PCM) / Immobilizer Control Module - Ignition Key Codes do not Match Incorrect/Damaged Key, PCM Incorrectly Programmed
P1623 Engine Control Module (PCM) - EEPROM Error PCM
P1624 Engine Control Module (PCM) - Immobilizer Deactivation Signal Missing Battery Disconnected - Erase Trouble Code, Immobilizer System Malfunction
P1627 PCM/ABS Electrical Connection - Communication Error Wiring, ABS Control Module, PCM
P1631 Alternator - Output Voltage Low Wiring, Alternator Drive Belt, Alternator
P1632 Engine Control Module (PCM) - Supply Voltage Low Wiring, Alternator, Battery
P1633 Engine Control Module (PCM) - Supply Voltage High Wiring, Voltage Surge when Battery Disconnected, Alternator
P1634 Alternator - Output Voltage High/Battery Voltage Low Wiring, Alternator, Battery
P1649 Engine Control Module (PCM) - Defective PCM
P1650 Power Steering Pressure (PSP) Switch Wiring, PSP Switch
P1720 Vehicle Speed Sensor (VSS) Wiring, Speedometer, VSS
P1743 Torque Converter Clutch (TCC) Solenoid Wiring, TCC Control Solenoid
P1744 Torque Converter Clutch (TCC) Solenoid Wiring, TCC Solenoid
P1765 Shift Timing Solenoid, 3-2 Wiring, Shift Timing Solenoid
P1770 Overrunning Clutch Solenoid Wiring, Overrunning Clutch Solenoid
P1790 Throttle Position (TP) Sensor Wiring, TP Sensor

Important Note: This sequence is for the Mazda variants listed in the Fault Code Table above. For other manufacturers, check if the vehicle is equipped with a 25-Pin DLC connector and also check to see if the above test can be carried out. Serious damage to the PCM will occur if the test is carried out on a vehicle that does not support the above test method. Refer to manufacturer's wiring and technical information for further information.

Fault code information reproduced by kind permission of Autodata.

AT173-3

Disclaimer
This help topic is subject to changes without notification. The information within is carefully checked and considered to be correct. This information is an example of our investigations and findings and is not a definitive procedure. Pico Technology accepts no responsibility for inaccuracies. Each vehicle may be different and require unique test settings.

Suitable accessories

  • Back-pinning Probe Set

    £48.00

  • Flexible Back-pinning Probe

    £7.00

  • Premium Test Lead: BNC to 4 mm, 3 m

    £48.00

  • Premium Test Leads: Set of four leads 3 m (TA125 - TA128)

    £179.00

Share your experience

If you have any suggestions to improve this guided test please do so using the 'add comment' button.

Add comment

Your email address will not be published. Required fields are marked *

Guided test: Mazda 25-Pin DLC