dashboard: expand CAN diagnostics

firmware/esp32-s3-dashboard/README.md

@@ -75,3 +75,14 @@ The dashboard uses field-filtered `/api/v1/status` calls:
 - Slow poll: `/api/v1/status?fields=network,system,config`
 
 This keeps the endpoint model simple while reducing payload size, JSON parsing, and UI churn.
+
+## OBD-II / CAN Diagnostics
+
+The hidden diagnostics overlay distinguishes raw CAN traffic from parsed
+OBD-II coolant responses. It reports request successes and failures, total
+raw frames received, the last frame identifier and DLC, TWAI queue depth,
+controller error counters, missed or overrun frames, arbitration losses,
+and bus errors.
+
+Raw RX activity confirms that the display is receiving CAN frames even when
+the vehicle does not return a matching Mode 01 PID 05 coolant response.

firmware/esp32-s3-dashboard/esp32-s3-dashboard.ino

@@ -47,7 +47,13 @@ static unsigned long last_obd_poll_ms = 0;
 static unsigned long last_obd_rx_ms = 0;
 static unsigned long last_obd_tx_ms = 0;
 static uint32_t obd_tx_count = 0;
+static uint32_t obd_tx_fail_count = 0;
 static uint32_t obd_rx_count = 0;
+static uint32_t obd_raw_rx_count = 0;
+static uint32_t obd_last_rx_identifier = 0;
+static uint8_t obd_last_rx_dlc = 0;
+static bool obd_last_rx_extended = false;
+static unsigned long last_obd_raw_rx_ms = 0;
 static int obd_coolant_temp_f = -999;
 static int last_rendered_obd_coolant_temp_f = -1000;
 static String obd_last_error = "not initialized";
@@ -491,6 +497,7 @@ static void send_obd_coolant_request()
         last_obd_tx_ms = millis();
         obd_last_error = "coolant request sent";
     } else {
+        obd_tx_fail_count++;
         obd_last_error = "tx failed: " + String((int)result);
     }
 }
@@ -539,6 +546,12 @@ static void process_obd_can()
 
     twai_message_t message = {};
     while (twai_receive(&message, 0) == ESP_OK) {
+        obd_raw_rx_count++;
+        obd_last_rx_identifier = message.identifier;
+        obd_last_rx_dlc = message.data_length_code;
+        obd_last_rx_extended = message.extd;
+        last_obd_raw_rx_ms = millis();
+
         handle_obd_can_message(message);
     }
 
@@ -625,15 +638,95 @@ static void update_diagnostics_overlay()
     text += "\n\nOBD-II / CAN\n";
     text += "  TWAI: ";
     text += obd_can_started ? "started" : "offline";
+    text += " @ 500 kbps";
     text += "\n  Pins: TX GPIO15 / RX GPIO16";
     text += "\n  Coolant: ";
     text += obd_coolant_temp_f > -100 ? String(obd_coolant_temp_f) + "°F" : String("--");
-    text += "\n  TX/RX: ";
+
+    text += "\n  Requests OK/fail: ";
     text += String(obd_tx_count);
     text += "/";
+    text += String(obd_tx_fail_count);
+
+    text += "\n  Raw RX/coolant RX: ";
+    text += String(obd_raw_rx_count);
+    text += "/";
     text += String(obd_rx_count);
-    text += "\n  Last RX age: ";
+
-    text += last_obd_rx_ms > 0 ? String((millis() - last_obd_rx_ms) / 1000) + "s" : String("--");
+    text += "\n  Last frame: ";
+    if (obd_raw_rx_count > 0) {
+        text += obd_last_rx_extended ? "EXT 0x" : "STD 0x";
+        text += String(obd_last_rx_identifier, HEX);
+        text += " DLC ";
+        text += String(obd_last_rx_dlc);
+    } else {
+        text += "--";
+    }
+
+    text += "\n  Raw RX age: ";
+    text += last_obd_raw_rx_ms > 0
+        ? String((millis() - last_obd_raw_rx_ms) / 1000) + "s"
+        : String("--");
+
+    text += "\n  Coolant RX age: ";
+    text += last_obd_rx_ms > 0
+        ? String((millis() - last_obd_rx_ms) / 1000) + "s"
+        : String("--");
+
+    if (obd_can_started) {
+        twai_status_info_t can_status = {};
+        esp_err_t status_result = twai_get_status_info(&can_status);
+
+        if (status_result == ESP_OK) {
+            const char *state_text = "unknown";
+
+            switch (can_status.state) {
+                case TWAI_STATE_STOPPED:
+                    state_text = "stopped";
+                    break;
+                case TWAI_STATE_RUNNING:
+                    state_text = "running";
+                    break;
+                case TWAI_STATE_BUS_OFF:
+                    state_text = "bus-off";
+                    break;
+                case TWAI_STATE_RECOVERING:
+                    state_text = "recovering";
+                    break;
+                default:
+                    break;
+            }
+
+            text += "\n  State: ";
+            text += state_text;
+
+            text += " TXq/RXq ";
+            text += String(can_status.msgs_to_tx);
+            text += "/";
+            text += String(can_status.msgs_to_rx);
+
+            text += "\n  TEC/REC: ";
+            text += String(can_status.tx_error_counter);
+            text += "/";
+            text += String(can_status.rx_error_counter);
+
+            text += "\n  Fail/miss/overrun: ";
+            text += String(can_status.tx_failed_count);
+            text += "/";
+            text += String(can_status.rx_missed_count);
+            text += "/";
+            text += String(can_status.rx_overrun_count);
+
+            text += "\n  Arb lost/bus errors: ";
+            text += String(can_status.arb_lost_count);
+            text += "/";
+            text += String(can_status.bus_error_count);
+        } else {
+            text += "\n  Driver status error: ";
+            text += String((int)status_result);
+        }
+    }
+
     text += "\n  Last status: ";
     text += obd_last_error;