I'm developing a React Native app that displays engine RPM almost in real-time by connecting to an ELM327 Bluetooth interface. I tested the ELM327 using the Piston app, and the latency is acceptable. However, when I send the ATZ command from my app, the ELM327's indicator light turns green, but I don't receive any data back. I also tried sending the 010C command, but I got no response either. Here are starting logs from Piston app: .png I'm using the react-native-bluetooth-serial library. Below is a code that sends only the ATZ command:

import { 
  View, 
  Text, 
  FlatList, 
  TouchableOpacity, 
  StyleSheet, 
  Alert, 
  PermissionsAndroid, 
  Platform 
} from 'react-native';
import RNBluetoothClassic, { BluetoothDevice } from 'react-native-bluetooth-classic';

const App = () => {
  const [devices, setDevices] = useState<BluetoothDevice[]>([]);
  const [selectedDevice, setSelectedDevice] = useState<BluetoothDevice | null>(null);
  const [response, setResponse] = useState<string>('');

  const requestBluetoothPermissions = async () => {
    if (Platform.OS === 'android') {
      try {
        const granted = await PermissionsAndroid.requestMultiple([
          PermissionsAndroid.PERMISSIONS.ACCESS_FINE_LOCATION,
          PermissionsAndroid.PERMISSIONS.BLUETOOTH_CONNECT,
          PermissionsAndroid.PERMISSIONS.BLUETOOTH_SCAN,
        ]);
        const allGranted = Object.values(granted).every(
          status => status === PermissionsAndroid.RESULTS.GRANTED
        );
        console.log('[APP] Permissions granted:', allGranted);
        return allGranted;
      } catch (error) {
        console.error('[APP] Error requesting permissions:', error);
        return false;
      }
    }
    return true;
  };

  const fetchPairedDevices = async () => {
    try {
      const pairedDevices = await RNBluetoothClassic.getBondedDevices();
      console.log('[APP] Paired devices:', pairedDevices);
      setDevices(pairedDevices);
    } catch (error) {
      Alert.alert('Error', 'Failed to fetch paired devices.');
      console.error('[APP] Error fetching devices:', error);
    }
  };

  useEffect(() => {
    const init = async () => {
      const permissionsGranted = await requestBluetoothPermissions();
      if (!permissionsGranted) {
        Alert.alert('Error', 'Bluetooth permissions not granted.');
        return;
      }
      const isEnabled = await RNBluetoothClassic.isBluetoothEnabled();
      if (!isEnabled) {
        Alert.alert('Error', 'Bluetooth is disabled.');
        return;
      }
      await fetchPairedDevices();
    };
    init();
  }, []);

  const readResponse = async (device: BluetoothDevice, timeout = 3000) => {
    let result = '';
    const start = Date.now();
    while (Date.now() - start < timeout && !result.includes('>')) {
      try {
        const chunk = await device.read();
        result += chunk;
      } catch (error) {
        console.error('[APP] Read error:', error);
        break;
      }
    }
    return result;
  };

  const connectAndSendATZ = async (device: BluetoothDevice) => {
    try {
      console.log('[APP] Connecting to:', device.name);
      const connected = await device.connect();
      if (connected) {
        console.log('[APP] Connected to:', device.name);
        setSelectedDevice(device);
        console.log('[APP -> ELM327] "ATZ"');
        await device.write('ATZ\r');
        setTimeout(async () => {
          try {
            const resp = await readResponse(device);
            console.log('[ELM327 -> APP] Response:', resp);
            setResponse(resp.toString());
          } catch (error) {
            console.error('[APP] Error reading response:', error);
          }
        }, 2000);
      } else {
        Alert.alert('Error', 'Failed to connect to the device.');
      }
    } catch (error) {
      Alert.alert('Connection Error', 'Failed to connect to the device.');
      console.error('[APP] Connection error:', error);
    }
  };

  return (
    <View style={styles.container}>
      <Text style={styles.title}>Select a Device</Text>
      {devices.length > 0 ? (
        <FlatList
          data={devices}
          keyExtractor={(item) => item.address}
          renderItem={({ item }) => (
            <TouchableOpacity 
              style={styles.deviceItem} 
              onPress={() => connectAndSendATZ(item)}
            >
              <Text style={styles.deviceName}>{item.name || 'Unknown Device'}</Text>
              <Text>{item.address}</Text>
            </TouchableOpacity>
          )}
        />
      ) : (
        <Text>No paired devices</Text>
      )}
      <Text style={styles.response}>Response: {response}</Text>
    </View>
  );
};

const styles = StyleSheet.create({
  container: { 
    flex: 1, 
    padding: 20, 
    backgroundColor: '#fff' 
  },
  title: { 
    fontSize: 24, 
    marginBottom: 20 
  },
  deviceItem: { 
    padding: 10, 
    borderBottomWidth: 1, 
    borderBottomColor: '#ccc' 
  },
  deviceName: { 
    fontSize: 18, 
    fontWeight: 'bold' 
  },
  response: { 
    marginTop: 20, 
    fontSize: 16 
  },
});

export default App;