CMD 0x56 - "Read errors"

  Error code stuff
  First byte serves as an index as follows:

  Index 01: read error code list. No Data. Answer ist the error code list
  using the following format:
  byte: Amount of error codes. That amount of times, there are the following
    bytes:
    byte: Error code numerical value.
    byte: Error code count-1 (how many time the failure condition was
      triggered until now).
  ...

  Example:
TX f4 03 56 01 a0 
RX 4f 0a d6 01 03 98 00 88 00 90 00 11

    Error codes:
    0x01 Defective control unit
    0x02 No start
    0x03 Flame failure
    0x04 Supply voltage too high
    0x05 Flame was detected prior to combustion
    0x06 Heating unit overheated  
    0x07 Heating unit interlocked
    0x08 Metering pumpu short circuit
    0x09 Combustion air fan short circuit
    0x0a Glow plug/flame monitor short circuit
    0x0b Circulation pump short circuit
    0x0c No comunication to air condition
    0x0d Green LED short circuit
    0x0e Yellow LED short circuit
    0x0f No configuraton signal
    0x10 Solenoid valve short circuit
    0x11 ECU wrong coded
    0x12 W-Bus comunication failure
    0x13 Vehicle fan relay short circuit
    0x14 Temperature sensor short circuit
    0x15 Combustion air fan blocked
    0x16 Battery main switch short circuit
    0x17 Invalid air flow reduction
    0x18 Comunication failure on customer specific bus
    0x19 Glow plug/electronic ignition short circuit
    0x1a Flame sensor short circuit
    0x1b Overheat short circuit
    0x1c Fault 28
    0x1d Solenoid valve shed test short circuit
    0x1e Fuel sensor short circuit
    0x1f Nozzle stock heating short circuit
    0x20 Operation indicator short circuit
    0x21 Flame indicator short circuit
    0x22 Reference resistance wrong
    0x23 Crash interlock activated
    0x24 Car is almost out of fuel
    0x25 Fuel pre heating short circuit
    0x26 PCB temperatur sensor short circuit
    0x27 Ground contact to the ECU broken
    0x28 Board net energy manager low power voltage
    0x29 Fuel priming still not done
    0x2a Error in the radio telegram
    0x2b Telestart still not programmed
    0x2c The pressure sensor has short circuit
    0x2d Fault 45
    ...
    0x31 Fault 49
    0x32 No start from control idle period
    0x33 Flame monitor signal invalid
    0x34 Default values entered
    0x35 EOL programming has not been carried out
    0x36 Thermal fuse short circuit
    0x37 Fault 55
    ...
    0x4f Fault 79
    0x50 User interface idle-Mode (no-communication)
    0x51 User interface has communication fault
    0x52 User interface send no defined operating mode
    0x53 Heater fan status message negative
    0x54 Heater fan status bus has short circuit to UB
    0x55 Temperature water sensor failure
    0x56 Temperature water sensor short circuit to UB
    0x57 Overheating water temperature sensor
    0x58 Overstepping water temperature sensor gradient
    0x59 Overheating blow temperature sensor
    0x5a Overstepping low temperature sensor gradient
    0x5b Overheating printed circuit board temperature sensor
    0x5c Overstepping printed circuit board temp sensor gradient
    0x5d Cabin temperature sensor failure
    0x5e Flame detector gradient failure
    0x5f Emergency cooling
    0x60 Customer specific fault 1
    ...
    0x7f Customer specific fault 32
    0x80 Fault 128
    0x81 EOL checksum error
    0x82 No start during test-run
    0x83 Flame failure
    0x84 Operating voltage too low
    0x85 Flame was detected after combustion
    0x86 Fault 134
    0x87 Heater lock-out permanent
    0x88 Fuel pump failure
    0x89 Combustion air fan interruption
    0x8a Glow plug / flame monitor interruption
    0x8b Circulation pump interruption
    0x8c Fault 140
    0x8d Green LED interruption
    0x8e Yellow LED interruption
    0x8f Fault 143
    0x90 Solenoid valve interruption
    0x91 Control unit locked or coded as neutral
    0x92 Command refresh failure
    0x93 Fault 147
    0x94 Temperature sensor interruption
    0x95 Combustion air fan tight
    0x96 Fault 150
    0x97 Overheat sensor position wrong
    0x98 Fault 152 (Power supply interruption)
    0x99 Glow plug / electronic ignition unit interruption
    0x9a Flame sensor interruption
    0x9b Setpoint transmitter invalid
    0x9c Intelligent undervoltage detection
    0x9d Solenoid valve shed test interruption
    0x9e Fuel sensor interruption
    0x9f Nozzle stock heating interruption
    0xa0 Operating indicator interruption
    0xa1 Flame indicator interruption
    0xa2 Fault 162
    ...
    0xa4 Fault 164
    0xa5 Fuel pre heating interruption
    0xa6 PCB temperature sensor interruption
    0xa7 Fault 167
    0xa8 Communication board net energy manager error
    0xa9 Fault 169
    0xaa Send on W-Bus not succeed
    0xab Overheat sensor interruption
    0xac The pressure sensor failure
    0xad Fault 173
    ...
    0xb5 Fault 181
    0xb6 Thermal fuse interrupted
    0xb7 Fault 183
    ...
    0xd0 Fault 208
    0xe0 Customer specific fault 33
    ...
    0xfe Customer specific fault 63
    0xff Unknown error code

  Index 02: Read complete error code block. 1 data byte corresponding to
  the error code numerical value.
    Format: 
      5 bytes: comprises status, counter, temperature, etc.
        1 byte status flags
          0x01 stored
          0x02 actual
        1 byte counter
        2 bytes operating state as command 0x50 index 7 byte 0,1
        1 byte Temperatur in Celcius offset 50 degree (value 70 -> 20 degrees)
      2 bytes: Power supply voltage during the incident in mili volt.
      2 bytes: Operating duration hours at the incident
      1 byte: Operating duration minutes at the incident

Example transaction
TX f4 04 56 02 98 3c 
RX 4f 0e d6 02 98 03 06 04 00 46 35 66 03 97 37 ba 

Error code count: 1
Error code 98, counter: 1
        State: 3
        Counter: 6
        Unkown values 4 0
        Temperatur 20 C
        Power supply tension: 0.870000
        Operating time: 14231:234


State: Not actual, not stored
Counter 1
Temperature 20 degrees Celcius
Operating State Off

Some more examples
TX f4 04 56 02 98 3c 
RX 4f 0e d6 02 98 00 01 04 00 46 35 66 03 97 1b 92
TX f4 04 56 02 88 2c
RX 4f 0e d6 02 88 00 01 04 00 46 35 7a 03 97 1d 98
TX f4 04 56 02 90 34
RX 4f 0e d6 02 90 00 01 04 00 46 35 66 03 97 1d 9c

  Index 03: Erase error codes. No data.

Empfangsbestätigung (CMD-Byte mit Bit 7 gesetzt).

TX: F4 03 24 .. .. 
RX: 4F 03 A4 .. ..