ELM322P View Datasheet(PDF) - Elm Electronics

Part Name

Description

Manufacturer

ELM322P

OBD (VPW) to RS232 Interpreter

Elm Electronics 

ELM322

Resetting Trouble Codes

The ELM322 is quite capable of resetting

diagnostic trouble codes, as this only requires issuing

a mode 04 command. The consequences should

always be considered before sending it, however, as

more than the MIL (or ‘Check Engine’ lamp) will be

reset. In fact, issuing a mode 04 will:

- reset the number of trouble codes

- erase any diagnostic trouble codes

- erase any stored freeze frame data

- erase the DTC that initiated the freeze frame

- erase all oxygen sensor test data

- erase mode 06 and 07 test results

Clearing of all of this information is not unique to

the ELM322, as it occurs whenever a scan tool is used

to reset your codes. Understand that the loss of this

data could cause your car to run poorly for a short time

while the system recalibrates itself.

To avoid inadvertently erasing stored information,

the SAE specifies that scan tools must verify that a

mode 04 is intended (“Are you sure?”) before actually

sending it to the vehicle, as all trouble code

information is immediately lost when the mode is sent.

Recall, though, that the ELM322 does not monitor the

content of messages, so it will not know to ask for

confirmation of the mode request – this would have to

be the duty of a software interface if one is written.

As stated, to actually erase diagnostic trouble

codes, one need only issue a mode 04 command. A

response of 44 from the vehicle indicates that the

mode request has been carried out, the information

erased, and the MIL turned off. Some vehicles may

require a special condition to occur (the ignition on but

the engine not running, etc.) before they will respond

to a mode 04 command.

That is all there is to clearing the codes. Once

again, be very careful not to inadvertently issue an 04!

Error Messages

When problems occur, the ELM322 will respond

with one of the following short messages. Here is a

brief description of each…

BUS BUSY

The ELM322 tried to send the mode command or

request for about 0.5 seconds without success.

Messages are all assigned priorities, which allows

one message to take precedence over another.

More important things may have been going on, so

try re-issuing your request.

BUS ERROR

An attempt was made to send a message, and the

data bus voltage did not change as expected. This is

most likely because of a circuit problem (a short or

open), so check all of your wiring carefully.

<DATA ERROR

There was a problem with the data checksum (CRC

byte), indicating a data error in the line pointed to

(the ELM322 still shows you what it received). There

could have been a circuit problem, or a noise burst

which interfered, so try re-sending the request again.

DATA ERROR

The ELM322 expects at least four bytes for every

message, and less than that were received. This

may have been caused by the key being turned off,

or a loose connection, for example, or by receiving a

single byte header message when a three byte

header was expected. Any monitoring that was in

progress will have been aborted. Try turning the

display of headers on to see what was actually sent.

NO DATA

There was no response from the vehicle before a

timeout occurred. The mode requested may not be

supported, so the vehicle ignored you, or the timeout

value was set too short, or possibly the ignition key

was not turned to the ‘on’ position. Try issuing an 01

00 command to be sure that the vehicle is ready to

receive commands, and if that works, try adjusting

the timeout to a longer value with the Set Timeout

AT command.

?

This is the standard response for a misunderstood

command received on the RS232 bus. Usually it is

due to a typing mistake.

ELM322DSF

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