diff --git a/proto/frequenz/api/common/v1/microgrid/communication_components/communication_components.proto b/proto/frequenz/api/common/v1/microgrid/communication_components/communication_components.proto
index 04e961e6..826c0f24 100644
--- a/proto/frequenz/api/common/v1/microgrid/communication_components/communication_components.proto
+++ b/proto/frequenz/api/common/v1/microgrid/communication_components/communication_components.proto
@@ -145,7 +145,7 @@ message CommunicationComponent {
 //     ```json
 //     {
 //       "diagnosticCode": "COMMUNICATION_COMPONENT_DIAGNOSTIC_CODE_CONFIGURATION_ERR",
-//       "vendorDiagnosticCode": 1002,
+//       "vendorDiagnosticCode": "ERR_1002",
 //       "message": "VLAN mismatch detected on port 3"
 //     }
 //     ```
@@ -160,7 +160,7 @@ message CommunicationComponentDiagnostic {
   CommunicationComponentDiagnosticCode diagnostic_code = 1;
 
   // Optional vendor-provided code for more granular diagnostics.
-  optional uint32 vendor_diagnostic_code = 2;
+  optional string vendor_diagnostic_code = 2;
 
   // Human-readable message providing additional context.
   string message = 3;
diff --git a/proto/frequenz/api/common/v1/microgrid/electrical_components/electrical_components.proto b/proto/frequenz/api/common/v1/microgrid/electrical_components/electrical_components.proto
index 758d8131..7c4a70e0 100644
--- a/proto/frequenz/api/common/v1/microgrid/electrical_components/electrical_components.proto
+++ b/proto/frequenz/api/common/v1/microgrid/electrical_components/electrical_components.proto
@@ -464,7 +464,7 @@ message ElectricalComponentConnection {
 //     {
 //       "diagnosticCode":
 //           "ELECTRICAL_COMPONENT_DIAGNOSTIC_CODE_OVERTEMPERATURE",
-//       "vendorDiagnosticCode": 2003,
+//       "vendorDiagnosticCode": "2003",
 //       "message": "Temperature sensor 3 reported 61.5°C (limit: 60°C)"
 //     }
 //     ```
@@ -485,7 +485,7 @@ message ElectricalComponentDiagnostic {
 
   // Optional vendor-provided error code for the error, for vendor-specific
   // insights or more granular diagnostics.
-  optional uint32 vendor_diagnostic_code = 2;
+  optional string vendor_diagnostic_code = 2;
 
   // Optional human-readable message providing additional context.
   string message = 3;
diff --git a/proto/frequenz/api/common/v1/microgrid/sensors/sensors.proto b/proto/frequenz/api/common/v1/microgrid/sensors/sensors.proto
index 0ab2c1da..93b78096 100644
--- a/proto/frequenz/api/common/v1/microgrid/sensors/sensors.proto
+++ b/proto/frequenz/api/common/v1/microgrid/sensors/sensors.proto
@@ -76,7 +76,7 @@ message Sensor {
 //     {
 //       "diagnosticCode":
 //           "SENSOR_DIAGNOSTIC_CODE_INTERNAL",
-//       "vendorErrorCode": 2003,
+//       "vendorErrorCode": "2003",
 //       "message": "Temperature sensor 3 reported 61.5°C (limit: 60°C)"
 //     }
 //     ```
@@ -91,7 +91,7 @@ message SensorDiagnostic {
 
   // Optional vendor-provided diagnostic code for the error, for vendor-specific
   // insights or more granular diagnostics.
-  optional uint32 vendor_diagnostic_code = 2;
+  optional string vendor_diagnostic_code = 2;
 
   // Optional human-readable message providing additional context.
   string message = 3;