User's Guide

PID Type Value Metric
0 (0x00) internal 0.000000
4 (0x04) internal 95.000000 v.b.soc
5 (0x05) metric 16.000000 v.b.temp
10 (0x0a) script 0.000000
11 (0x0b) unimplemented 0.000000
12 (0x0c) internal 0.000000 v.m.rpm
13 (0x0d) internal 0.000000 v.p.speed
16 (0x10) internal 13.708791 v.b.12v.voltage
32 (0x20) internal 0.000000
Types:
"internal" means default internal handling of the PID.
"metric" means a user-set mapping of PID to the named metric
"unimplemented" are PIDs requested by the device, but for which no map has been set
“script" means the user has configured a script to handle the PID
Special handling
Several PIDs are handled specially by the OBDII ECU task.
PIDs 0 and 32 are bit masks that indicate what other PIDs are being reported by the OBDII ECU
task. These are maintained internally based on the default, mapped, and scripted PID table.
Note that some OBDII devices use PID 0 as a test for ECU presence and operating mode
(standard or extended), and ignore the returned values. The OBDII ECU task supports both
modes.
PID 12, Engine RPM, is often monitored by the OBDII device to detect when the car is turned
off. Since an EV's motor is not rotating when the car is stopped, a HUD may decide to power
down when it sees the RPM drop below a particular value, or if there is no variation (jitter) in its
value. To prevent this, the OBDII ECU task will source a fake value of 500 rpm, plus a small
periodic variation, if the car is not moving (vehicle speed is less than 1). To actually let the
device turn off, see "External Power Control", below.
PID 16, MAF Air Flow, is commonly used by OBDII devices to display fuel flow, by measuring
the amount of air entering the engine in support of combustion. Since this is irrelevant to an EV,
the OBDII ECU task maps this metric to a simple integer. Most HUDs displays limit this to a
range of 0-19.9 liter/hr, which is acceptable to display the +12v battery voltage. Since the
conversion factors are complicated, this value is at best approximate, in spite of its implied
precision.
OVMS v3 User Guide Page 76 / 86