PassThruWriteMsgs v4.04

Sending messages

Last updated: January 11, 2026

Description

The function transmits messages over the diagnostic protocol. The adapter's transmit queue holds 50 messages per queue for a single channel and provides 64 KB of free memory for all queues. When a queue or all free memory is full, acceptance of new messages into the transmit queue is suspended.

long PassThruWriteMsg(unsigned long ChannelID, PASSTHRU_MSG *pMsg, unsigned long *pNumMsgs, unsigned long Timeout)

Important: For the ISO 15765 protocol, you must set up a Flow Control filter using PassThruStartMsgFilter before transmitting messages. Without it, the function returns the error ERR_NO_FLOW_CONTROL.

Parameters

unsigned long ChannelID - The channel identifier obtained from the PassThruConnect command.
PASSTHRU_MSG* pMsg - Pointer to an array of message structures. Messages to be transmitted over the diagnostic protocol are taken from this array.
unsigned long* pNumMsgs - Pointer to a variable holding the number of messages requested for transmission. After the function completes, the number of messages actually transmitted is written to this variable.
unsigned long Timeout - Timeout in milliseconds. If, after the timeout expires, the number of messages actually transmitted does not match the number requested, the error code ERR_TIMEOUT is returned. If the timeout is 0, the messages are placed into the transmit queue without waiting for physical transmission, and the function returns immediately. In this case the ERR_TIMEOUT error is not generated.

Return error codes

Code	Description	Possible causes and solutions
STATUS_NOERROR	Function completed successfully	—
ERR_DEVICE_NOT_CONNECTED	No connection to the adapter	The adapter is turned off or the connection has been lost Solution: Check the adapter power and the network/BLE connection The IP address is set incorrectly Solution: Check the connection parameters in PassThruOpen
ERR_INVALID_CHANNEL_ID	A non-existent ChannelID channel identifier was specified	ChannelID was not obtained from PassThruConnect Solution: Use the ChannelID returned by PassThruConnect The channel was closed via PassThruDisconnect Solution: Reopen the channel via PassThruConnect
ERR_NULL_PARAMETER	The pMsg or pNumMsgs pointer is not set	NULL was passed instead of a pointer Solution: Pass a valid pointer to the message array and to the count variable
ERR_TIMEOUT	Not all messages could be transmitted within the specified time	Too many messages or too short a timeout Solution: Increase the Timeout value or reduce the number of messages Bus problems (no CAN acknowledgement) Solution: Check the connection to the vehicle and the bus state
ERR_INVALID_MSG	Invalid message structure in pMsg	Incorrect message data or size Solution: Check the DataSize, Data and TxFlags fields in the PASSTHRU_MSG structure
ERR_MSG_PROTOCOL_ID	The protocol in the message does not match the channel protocol	ProtocolID in the message structure differs from the one specified in PassThruConnect Solution: Set pMsg->ProtocolID to the same protocol that was used when opening the channel
ERR_NO_FLOW_CONTROL	No Flow Control filter is set for the ISO 15765 protocol	Attempt to transmit an ISO 15765 message without a configured filter Solution: Call PassThruStartMsgFilter with the FLOW_CONTROL_FILTER type before transmitting
ERR_BUFFER_FULL	The transmit queue is full	Too many messages in the queue (limit: 50 messages, 64 KB) Solution: Wait for the previous messages to be sent or clear the queue via PassThruIoctl(CLEAR_TX_BUFFER)
ERR_FAILED	Internal error in the library or adapter	Memory allocation error or stack failure Solution: Call `PassThruGetLastError()` to get details

Examples

C/C++ example

#include "j2534_dll.hpp"

// ChannelID obtained earlier from PassThruConnect
unsigned long ChannelID;
PASSTHRU_MSG Msg;
unsigned long NumMsgs = 1;
unsigned long Timeout = 200;

// Building an ISO 15765 message (request SID 0x22, PID 0xF190)
Msg.ProtocolID = ISO15765;
Msg.TxFlags = ISO15765_FRAME_PAD;
Msg.Data[0] = 0x00;
Msg.Data[1] = 0x00;
Msg.Data[2] = 0x07;
Msg.Data[3] = 0xDF;
Msg.Data[4] = 0x22;
Msg.Data[5] = 0xF1;
Msg.Data[6] = 0x90;
Msg.DataSize = 7;

long ret = PassThruWriteMsg(ChannelID, &Msg, &NumMsgs, Timeout);
if (ret != STATUS_NOERROR) {
    char error[256];
    PassThruGetLastError(error);
    // Error handling
}

Kotlin example (Android)

// channelID obtained earlier from ptConnect
val msg = PassThruMsg(
    protocolID = ISO15765,
    dataSize = 7,
    txFlags = ISO15765_FRAME_PAD,
    // VIN request (SID 0x22, PID 0xF190)
    data = byteArrayOf(0x00, 0x00, 0x07, 0xDF.toByte(), 0x22, 0xF1.toByte(), 0x90.toByte())
)

val messages = arrayOf(msg)
val timeout = 200 // ms

val result = j2534.ptWriteMsgs(channelID, messages, timeout)
if (result.status == STATUS_NOERROR) {
    Log.i("J2534", "Messages sent: ${result.numMsgs}")
} else {
    Log.e("J2534", "Send error: ${result.status}")
}

Python example

# channel_id obtained earlier from PassThruConnect
msg = PassThruMsg()
msg.ProtocolID = ISO15765
msg.TxFlags = ISO15765_FRAME_PAD
msg.Data = bytes([0x00, 0x00, 0x07, 0xDF, 0x22, 0xF1, 0x90])
msg.DataSize = 7

num_msgs = ctypes.c_ulong(1)
timeout = 200  # ms

ret = j2534.PassThruWriteMsg(channel_id, ctypes.byref(msg), ctypes.byref(num_msgs), timeout)
if ret == 0:  # STATUS_NOERROR
    print(f"Messages sent: {num_msgs.value}")
else:
    print(f"Send error: {ret}")

C# example

// channelId obtained earlier from PassThruConnect
var msg = new PassThruMsg {
    ProtocolID = ISO15765,
    TxFlags = ISO15765_FRAME_PAD,
    Data = new byte[] { 0x00, 0x00, 0x07, 0xDF, 0x22, 0xF1, 0x90 },
    DataSize = 7
};

uint numMsgs = 1;
uint timeout = 200; // ms

int ret = J2534.PassThruWriteMsg(channelId, ref msg, ref numMsgs, timeout);
if (ret == 0) {
    Console.WriteLine($"Messages sent: {numMsgs}");
} else {
    Console.WriteLine($"Send error: {ret}");
}