DIALOG reference: glossary, OBD and UDS services, ISO-TP and PIDs

A reference for the terms and file types used across the DIALOG guides. It lists the OBD modes and UDS services DIALOG can request and the standard OBD-II PIDs. It also shows how ISO-TP splits long diagnostic messages into CAN frames.

Glossary

OBD modes and UDS services

The Mode field in DIALOG's PID settings takes one of these service numbers. Numbers 01 to 0A are OBD-II modes (SAE J1979). Numbers 10 and above are UDS services (ISO 14229). A positive reply adds 40 hex to the number, so a mode 01 request is answered with 41 and a service 22 request with 62.

To set up a REBEL to poll these, see DIALOG: log UDS and OBD diagnostic data. For the background, read understanding UDS and on-board diagnostics basics.

ISO-TP frame types

A classic CAN frame carries at most 8 bytes, so a diagnostic message that is longer travels in pieces under ISO 15765-2 (ISO-TP). The first byte of each frame, byte 0, holds the protocol control information (PCI). Its upper four bits give the frame type. Bytes are counted from 0, as in the diagram below.

Single frame (SF)

A short message that fits in one frame. Its data length (DL) is the lower four bits of byte 0, up to 7 bytes on classic CAN. The PCI byte is not counted in the length.

First frame (FF)

Starts a long message, which is then split over several frames. DL high and DL low together hold the length in 12 bits, so a message can be up to 4,095 bytes. The sender of the segmented message sends one first frame per message.

Flow control frame (FC)

Sent by the receiver of a long message, in reply to the first frame and after each block of consecutive frames, to pace the sender. Its flow status (FS) takes one of three values. FS 0, clear to send (CTS), lets the sender carry on using BS max and ST min. FS 1, wait (WT), pauses the sender until a clear to send arrives. An ECU accepts a wait but does not send one. FS 2 means overflow.

Block size (BS max)

The most consecutive frames the sender may send before it waits for the next flow control frame. 0 means no further flow control frames. The sender sends the rest, spaced by ST min.

Separation time (ST min)

The minimum gap between consecutive frames, in milliseconds. It applies between consecutive frames only, not between a flow control frame and the next consecutive frame.

Consecutive frame (CF)

Carries the rest of a long message. The receiver assembles the data bytes until the whole message has arrived. Its sequence number (SN) counts the frames, 1 to 15 then 0 again, so lost or duplicated frames are detected.

Standard OBD-II PIDs

These are the mode 01 parameter IDs defined by SAE J1979. A vehicle supports a subset. PIDs 00, 20, 40 and so on return a bit mask of the PIDs it supports in the next range. The OBD presets in DIALOG's PID library use these numbers.

This table follows SAE J1979. It corrects these errors in earlier documentation:

• PID 06 was printed as 09.
• PIDs 0F and 10 had their units swapped.
• PID 1A was given as bank 3.
• Several units and descriptions were incomplete.

All 132 standard OBD-II PIDs

Standard OBD-II mode 01 PIDs

PID (hex)	Symbol	Units	Description
00			Supported PIDs 01 to 20
01			Status since DTCs cleared (includes MIL and DTC status and number)
02			Freeze DTC
03	FUELSYS		Fuel system status
04	LOAD_PCT	%	Calculated engine load value
05	ECT	°C	Engine coolant temperature
06	SHRTFT1	%	Short term fuel trim (bank 1)
07	LONGTFT1	%	Long term fuel trim (bank 1)
08	SHRTFT2	%	Short term fuel trim (bank 2)
09	LONGTFT2	%	Long term fuel trim (bank 2)
0A	FRP	kPa	Fuel pressure
0B	MAP	kPa	Intake manifold absolute pressure
0C	RPM	rpm	Engine speed
0D	VSS	km/h	Vehicle speed
0E	SPARKADV	° before TDC	Timing advance (cylinder 1)
0F	IAT	°C	Intake air temperature
10	MAF	g/s	Mass air flow rate
11	TP	%	Throttle position
12			Commanded secondary air status
13			Oxygen sensors present (two banks)
14	O2S11	V	Oxygen sensor 1 (bank 1)
15	O2S12	V	Oxygen sensor 2 (bank 1)
16	O2S13	V	Oxygen sensor 3 (bank 1)
17	O2S14	V	Oxygen sensor 4 (bank 1)
18	O2S21	V	Oxygen sensor 1 (bank 2)
19	O2S22	V	Oxygen sensor 2 (bank 2)
1A	O2S23	V	Oxygen sensor 3 (bank 2)
1B	O2S24	V	Oxygen sensor 4 (bank 2)
1C			OBD standard vehicle compliancy
1D			Oxygen sensors present (four banks)
1E	PTO_STAT		Auxiliary input status
1F		s	Run time since engine start
20			Supported PIDs 21 to 40
21	MIL_DIST	km	Distance travelled with MIL on
22		kPa	Fuel rail pressure (relative to manifold vacuum)
23	FRP_FF	kPa	Fuel rail pressure (diesel or gasoline direct injection)
24		V	Oxygen sensor 1: equivalence ratio and voltage
25		V	Oxygen sensor 2: equivalence ratio and voltage
26		V	Oxygen sensor 3: equivalence ratio and voltage
27		V	Oxygen sensor 4: equivalence ratio and voltage
28		V	Oxygen sensor 5: equivalence ratio and voltage
29		V	Oxygen sensor 6: equivalence ratio and voltage
2A		V	Oxygen sensor 7: equivalence ratio and voltage
2B		V	Oxygen sensor 8: equivalence ratio and voltage
2C		%	Commanded exhaust gas recirculation
2D		%	Exhaust gas recirculation error
2E		%	Commanded evaporative purge
2F	FLI	%	Fuel tank level input
30			Number of warm-ups since codes cleared
31		km	Distance travelled since codes cleared
32		Pa	Evaporative system vapour pressure
33	BARO	kPa	Barometric pressure
34		mA	Oxygen sensor 1: equivalence ratio and current
35		mA	Oxygen sensor 2: equivalence ratio and current
36		mA	Oxygen sensor 3: equivalence ratio and current
37		mA	Oxygen sensor 4: equivalence ratio and current
38		mA	Oxygen sensor 5: equivalence ratio and current
39		mA	Oxygen sensor 6: equivalence ratio and current
3A		mA	Oxygen sensor 7: equivalence ratio and current
3B		mA	Oxygen sensor 8: equivalence ratio and current
3C	CATEMP11	°C	Catalyst temperature sensor 1 (bank 1)
3D	CATEMP21	°C	Catalyst temperature sensor 1 (bank 2)
3E	CATEMP12	°C	Catalyst temperature sensor 2 (bank 1)
3F	CATEMP22	°C	Catalyst temperature sensor 2 (bank 2)
40			Supported PIDs 41 to 60
41			Monitor status (this drive cycle)
42	VPWR	V	Control module voltage
43	LOAD_ABS	%	Absolute load value
44	EQ_RAT		Commanded equivalence ratio
45	TP_REL	%	Relative throttle position
46	AAT	°C	Ambient air temperature
47		%	Absolute throttle position B
48		%	Absolute throttle position C
49		%	Accelerator pedal position D
4A		%	Accelerator pedal position E
4B		%	Accelerator pedal position F
4C		%	Commanded throttle actuator
4D		min	Time run with MIL on
4E		min	Time since DTCs cleared
51			Fuel type
52		%	Ethanol fuel
53		kPa	Absolute evaporative system vapour pressure
54		Pa	Evaporative system vapour pressure
55			Short-term secondary oxygen sensor trim (bank 1 and 3)
56			Long-term secondary oxygen sensor trim (bank 1 and 3)
57			Short-term secondary oxygen sensor trim (bank 2 and 4)
58			Long-term secondary oxygen sensor trim (bank 2 and 4)
59		kPa	Absolute fuel rail pressure
5A		%	Relative accelerator pedal position
5B		%	Hybrid battery pack remaining life
5C		°C	Engine oil temperature
5D			Fuel injection timing
5E		L/h	Engine fuelling rate
5F			Emission requirements vehicle designed to meet
61			Driver engine demand
62		%	Actual engine torque
63			Engine reference torque
64		%	Engine torque
65			Auxiliary in/output supported
66			Mass airflow sensor
67		°C	Engine coolant temperature
68		°C	Intake air temperature sensor
69			Commanded exhaust gas recirculation and EGR error
6A			Commanded diesel intake, airflow control and relative intake airflow position
6B		°C	Exhaust gas recirculation temperature
6C			Commanded throttle actuator control and relative throttle position
6D			Fuel pressure control system
6E			Injection pressure control system
6F			Turbocharger compressor inlet pressure
70			Boost pressure control
71			Variable geometry turbine control
72			Wastegate control
73			Exhaust pressure
74		rpm	Turbocharger speed
75		°C	Turbocharger temperature
76		°C	Turbocharger temperature
77		°C	Charge air cooler temperature
78		°C	Exhaust gas temperature (bank 1)
79		°C	Exhaust gas temperature (bank 2)
7A			Diesel particulate filter
7B			Diesel particulate filter
7C			Diesel particulate filter
7D			NOx NTE control area status
7E			Particulate matter NTE control area status
7F			Engine run time
81			Engine run time for the auxiliary emissions control device
82			Engine run time for the auxiliary emissions control device
83			NOx sensor
84		°C	Manifold surface temperature
85			NOx reagent system
86			Particulate matter sensor
87		kPa	Absolute intake manifold pressure

To log a PID, see DIALOG: log UDS and OBD diagnostic data. If you have a REXGEN, you can log the same PIDs with REXDESK. See REXGEN: log OBD2 Mode 1 PIDs.

Next: DIALOG: what it does, versions and system requirements.