ELM327
Error Messages and Alerts
The following shows what the ELM327 will send to
warn you of a condition or a problem. Some of these
messages do not appear if using the automatic search
for a protocol, or if the Programmable Parameter bits
disable them.
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circuit, then check all of the voltage levels at the
offending OBD input, as this error is very likely due to
a wiring problem (see our ‘AN02 - ELM327 Circuit
Construction’ for some typical voltages).
This is the standard response for a misunderstood
command received on the RS232 input. Usually it is
due to a typing mistake, but it can also occur if you try
to do something that is not appropriate (eg. trying to do
an AT FI command if you are not set for protocol 5).
BUS ERROR
A generic problem has occurred. This is most
often from an invalid signal being detected on the bus
(for example, a pulse that is longer than a valid Break
signal), but usually is from a wiring error. Note that
some vehicles may generate long pulses as part of
their startup process, so you may see this message as
part of a normal vehicle startup while ‘monitoring all.’
ACT ALERT or !ACT ALERT
This message occurs as a warning that there has
been no RS232 or OBD activity for some time (see the
Power Control section for details). If allowed, the IC
will be initiating a switch to the Low Power (standby)
mode of operation. If this was initiated by no RS232
activity, sending something within the next minute will
stop the switch to low power. Note that !ACT ALERT is
printed if PP 0F bit 1 is 1.
CAN ERROR
The CAN system had difficulty initializing, sending,
or receiving. Often this is simply from not being
connected to a CAN system when you attempt to send
a message, but it may be because you have set the
system to an incorrect protocol, or to a baud rate that
does not match the actual data rate. As with BUS
ERRORs, the CAN ERROR might also be the result of
a wiring problem, so if this is the first time using your
ELM327 circuit, review all of your CAN interface
circuitry before proceeding.
BUFFER FULL
The ELM327 provides a 512 byte internal RS232
transmit buffer so that OBD messages can be received
quickly, stored, and sent to the computer at a more
constant rate. Occasionally (particularly with CAN
systems) the buffer will fill at a faster rate than it is
being emptied by the PC. Eventually it may become
full, and no more data can be stored (it is lost).
If you are receiving BUFFER FULL messages,
and you are using a lower baud data rate, give serious
consideration to changing your data rate to something
higher. If you still receive BUFFER FULL messages
after that, you might consider turning the headers and
maybe the spaces off (with AT H0, and AT S0), or
using the CAN filtering commands (AT CRA, or CM
and CF) to reduce the amount of data being sent.
DATA ERROR
There was a response from the vehicle, but the
information was incorrect or could not be recovered.
<DATA ERROR
There was an error in the line that this points to,
either from an incorrect checksum, or a problem with
the format of the message (the ELM327 still shows
you what it received). There could have been a noise
burst which interfered, possibly a circuit problem, or
perhaps you have the CAN Auto Formatting (CAF) on
and you are looking at a system that is not of the
ISO 15765-4 format. Try resending the command
again – if it was a noise burst, it may be received
correctly the second time.
BUS BUSY
This occurs when the ELM327 tries to send a
message, or to initialize the bus, and detects too much
activity to do so (it needs a pause in activity in order to
insert the message). Although this could be because
the bus was in fact very busy, it is almost always due
to a wiring problem that is giving a continuously active
input. If this is an initial trial with your new ELM327
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