ELM timeout while calling any function eg .rpm() if ELM RX TX is connected with wire to Arduino

[Som4567]

Every time I tried to connect ELM with Arduino ( UNO or Mega) it successfully gets connected to ELM but the moment it calls any function it gives error 'ELM timeout'

I face this issue only with the wire connection of RX and TX. If I use FTDI wire to directly read from ELM using ScanTool then it works perfectly.
It works perfectly with BLE and wifi.

I am using 38400 baud rate for ELM port.

[PowerBroker2]

Please post your code and all debug printouts

[Som4567]

Hi @PowerBroker2

sorry for delay in response. I was out of town so couldn't check it earlier.
Please find attached log.
ELM_output_debug.txt

[PowerBroker2]

Looks like you're communicating with the ELM327 successfully, however, the ELM327 can't get the info it needs from the car. Hence the "SEARCHING...UNABLE TO CONNECT". Most likely you need to specify a protocol that works for your vehicle:

ELMduino/src/ELMduino.h

Lines 7 to 22 in ad580d9

	//-------------------------------------------------------------------------------------//
	// Protocol IDs
	//-------------------------------------------------------------------------------------//
	const char AUTOMATIC = '0';
	const char SAE_J1850_PWM_41_KBAUD = '1';
	const char SAE_J1850_PWM_10_KBAUD = '2';
	const char ISO_9141_5_BAUD_INIT = '3';
	const char ISO_14230_5_BAUD_INIT = '4';
	const char ISO_14230_FAST_INIT = '5';
	const char ISO_15765_11_BIT_500_KBAUD = '6';
	const char ISO_15765_29_BIT_500_KBAUD = '7';
	const char ISO_15765_11_BIT_250_KBAUD = '8';
	const char ISO_15765_29_BIT_250_KBAUD = '9';
	const char SAE_J1939_29_BIT_250_KBAUD = 'A';
	const char USER_1_CAN = 'B';
	const char USER_2_CAN = 'C';

You can do so by specifying a protocol in the begin() function:

ELMduino/src/ELMduino.cpp

Lines 6 to 25 in ad580d9

	/*
	bool ELM327::begin(Stream &stream, const bool& debug, const uint16_t& timeout, const char& protocol, const uint16_t& payloadLen)
	Description:
	------------
	* Constructor for the ELM327 Class; initializes ELM327
	Inputs:
	-------
	* Stream &stream - Pointer to Serial port connected to ELM327
	* bool debug - Specify whether or not to print debug statements to "Serial"
	* uint16_t timeout - Time in ms to wait for a query response
	* char protocol - Protocol ID to specify the ELM327 to communicate with the ECU over
	* uint16_t payloadLen - Maximum number of bytes expected to be returned by the ELM327 after a query
	Return:
	-------
	* bool - Whether or not the ELM327 was propperly
	initialized
	*/

[Som4567]

@PowerBroker2 thanks a lot for your support. It was a wiring issue with MCP2551. Now I can communicate with ELM.

[MGC1STOKI]

Im having the same issue with my wired ELM327 even after selecting the correct protocol:

#include <SoftwareSerial.h>
#include "ELMduino.h"


SoftwareSerial mySerial(11, 12); // RX, TX
#define ELM_PORT mySerial


ELM327 myELM327;


float voltage;
char protocol = ISO_15765_11_BIT_500_KBAUD;

void setup()
{
  Serial.begin(115200);
  ELM_PORT.begin(38400);
  myELM327.begin(ELM_PORT, protocol);
  Serial.println("Attempting to connect to ELM327...");

  if (!myELM327.begin(ELM_PORT))
  {
    Serial.println("Couldn't connect to OBD scanner");
    while (1);
  }
  Serial.println("Connected to ELM327");
  delay(2000);
  if (myELM327.sendCommand(DISP_CURRENT_PROTOCOL) == ELM_SUCCESS)
  {
    Serial.print("PROTOCOL: ");
    Serial.println(myELM327.payload);
  }

}


void loop()
{
  float tempVoltage = myELM327.ctrlModVoltage();

  if (myELM327.status == ELM_SUCCESS)
  {
    voltage = tempVoltage;
    Serial.print("Volatage: "); 
    Serial.print(voltage);
    Serial.println(" v");
  }
  else
  {
    Serial.print(F("\tERROR: "));
    Serial.println(myELM327.status);
    delay(100);
    
  }
}

Using the DISP_CURRENT_PROTOCOL command to check what protocol it should be using shows that it is still set to auto even after setting it in the begin() function.
The log shows that it is still sending AT TP A0 when presumably i would expect it to send AT TP A6.

I know this is definitely the right protocol for my car as it is what the Torque app works with when set.

19:40:34.197 -> Clearing input serial buffer
19:40:34.197 -> Sending the following command/query: AT D
19:40:34.235 -> Received char: \r
19:40:34.235 -> Received char: O
19:40:34.235 -> Received char: K
19:40:34.235 -> Received char: \r
19:40:34.235 -> Received char: \r
19:40:34.235 -> Received char: >
19:40:34.235 -> Delimiter found
19:40:34.235 -> All chars received: OK
19:40:34.340 -> Clearing input serial buffer
19:40:34.340 -> Sending the following command/query: AT Z
19:40:34.340 -> Received char: ⸮
19:40:34.340 -> Received char: ⸮
19:40:34.340 -> Received char: i
19:40:34.340 -> Received char: ⸮
19:40:34.340 -> Received char: \r
19:40:35.140 -> Received char: \r
19:40:35.140 -> Received char: \r
19:40:35.140 -> Received char: E
19:40:35.140 -> Received char: L
19:40:35.140 -> Received char: M
19:40:35.140 -> Received char: 3
19:40:35.140 -> Received char: 2
19:40:35.140 -> Received char: 7
19:40:35.140 -> Received char:
19:40:35.140 -> Received char: v
19:40:35.140 -> Received char: 1
19:40:35.140 -> Received char: .
19:40:35.140 -> Received char: 5
19:40:35.140 -> Received char: \r
19:40:35.140 -> Received char: \r
19:40:35.140 -> Received char: >
19:40:35.140 -> Delimiter found
19:40:35.177 -> All chars received: iELM327v15
19:40:35.250 -> Clearing input serial buffer
19:40:35.250 -> Sending the following command/query: AT E0
19:40:35.250 -> Received char: ⸮
19:40:35.250 -> Received char: ⸮
19:40:35.250 -> Received char: +
19:40:35.250 -> Received char: ⸮
19:40:35.250 -> Received char: 5
19:40:35.250 -> Received char: ⸮
19:40:35.250 -> Received char: O
19:40:35.250 -> Received char: K
19:40:35.250 -> Received char: \r
19:40:35.250 -> Received char: \r
19:40:35.285 -> Received char: >
19:40:35.285 -> Delimiter found
19:40:35.285 -> All chars received: 5OK
19:40:35.359 -> Clearing input serial buffer
19:40:35.359 -> Sending the following command/query: AT S0
19:40:35.392 -> Received char: O
19:40:35.392 -> Received char: K
19:40:35.392 -> Received char: \r
19:40:35.392 -> Received char: \r
19:40:35.392 -> Received char: >
19:40:35.392 -> Delimiter found
19:40:35.392 -> All chars received: OK
19:40:35.496 -> Clearing input serial buffer
19:40:35.496 -> Sending the following command/query: AT AL
19:40:35.496 -> Received char: O
19:40:35.496 -> Received char: K
19:40:35.496 -> Received char: \r
19:40:35.496 -> Received char: \r
19:40:35.496 -> Received char: >
19:40:35.496 -> Delimiter found
19:40:35.496 -> All chars received: OK
19:40:35.602 -> Clearing input serial buffer
19:40:35.602 -> Sending the following command/query: AT TP A0
19:40:35.602 -> Received char: O
19:40:35.602 -> Received char: K
19:40:35.602 -> Received char: \r
19:40:35.602 -> Received char: \r
19:40:35.602 -> Received char: >
19:40:35.602 -> Delimiter found
19:40:35.602 -> All chars received: OK
19:40:35.602 -> Attempting to connect to ELM327...
19:40:36.954 -> Connected to ELM327
19:40:38.954 -> PROTOCOL: AUTO
19:40:39.970 -> ERROR: 7
19:40:41.066 -> ERROR: 7
19:40:41.171 -> Volatage: 0.00 v
19:40:42.169 -> ERROR: 7
19:40:43.291 -> ERROR: 7
19:40:43.364 -> Volatage: 0.00 v
19:40:44.379 -> ERROR: 7
19:40:45.495 -> ERROR: 7
19:40:46.586 -> ERROR: 7
19:40:47.672 -> ERROR: 7

[PowerBroker2]

myELM327.begin(ELM_PORT, protocol);

^ That is not a valid use of the library's begin() function. Please read the documentation and ensure you're using the latest version of the library:

ELMduino/src/ELMduino.cpp

Lines 6 to 26 in ad580d9

	/*
	bool ELM327::begin(Stream &stream, const bool& debug, const uint16_t& timeout, const char& protocol, const uint16_t& payloadLen)
	Description:
	------------
	* Constructor for the ELM327 Class; initializes ELM327
	Inputs:
	-------
	* Stream &stream - Pointer to Serial port connected to ELM327
	* bool debug - Specify whether or not to print debug statements to "Serial"
	* uint16_t timeout - Time in ms to wait for a query response
	* char protocol - Protocol ID to specify the ELM327 to communicate with the ECU over
	* uint16_t payloadLen - Maximum number of bytes expected to be returned by the ELM327 after a query
	Return:
	-------
	* bool - Whether or not the ELM327 was propperly
	initialized
	*/
	bool ELM327::begin(Stream &stream, const bool& debug, const uint16_t& timeout, const char& protocol, const uint16_t& payloadLen)

[PowerBroker2]

This line is also incorrect:

char protocol = ISO_15765_11_BIT_500_KBAUD;

[MGC1STOKI]

update - changing myELM327.begin(ELM_PORT, protocol); to myELM327.begin(ELM_PORT, true, 1000, protocol); did produce an AT TP A6 but with the same result (error 7 repeating with the occasional response of 0 voltage)

[MGC1STOKI]

changing char protocol = ISO_15765_11_BIT_500_KBAUD; to char protocol = "ISO_15765_11_BIT_500_KBAUD" produces this respose:

19:58:31.628 -> Clearing input serial buffer
19:58:31.628 -> Sending the following command/query: AT TP A⸮
19:58:31.628 -> Received char: ?
19:58:31.628 -> Received char: \r
19:58:31.628 -> Received char: \r
19:58:31.628 -> Received char: >
19:58:31.628 -> Delimiter found
19:58:31.628 -> All chars received:
19:58:31.628 -> Setting protocol via AT TP A%c did not work - trying via AT SP %c
19:58:31.628 -> Clearing input serial buffer
19:58:31.628 -> Sending the following command/query: AT SP ⸮
19:58:31.662 -> Received char: ?
19:58:31.662 -> Received char: \r
19:58:31.662 -> Received char: \r
19:58:31.662 -> Received char: >
19:58:31.662 -> Delimiter found
19:58:31.662 -> All chars received:
19:58:31.662 -> Setting protocol via AT SP %c did not work
19:58:31.662 -> Attempting to connect to ELM327...
19:58:32.990 -> Connected to ELM327

[PowerBroker2]

This is worse:

char protocol = "ISO_15765_11_BIT_500_KBAUD"

Try this instead:

myELM327.begin(ELM_PORT, true, 1000, ISO_15765_11_BIT_500_KBAUD);

[MGC1STOKI]

myELM327.begin(ELM_PORT, true, 1000, ISO_15765_11_BIT_500_KBAUD); produces the same response