AUX_CHANNEL_OPERATION_FAILED_REASON_UNKNOWN,
        AUX_CHANNEL_OPERATION_FAILED_INVALID_REPLY,
        AUX_CHANNEL_OPERATION_FAILED_TIMEOUT,
-       AUX_CHANNEL_OPERATION_FAILED_HPD_DISCON
+       AUX_CHANNEL_OPERATION_FAILED_HPD_DISCON,
+       AUX_CHANNEL_OPERATION_FAILED_ENGINE_ACQUIRE
 };
 
 
 
        memset(&aux_rep, 0, sizeof(aux_rep));
 
        aux_engine = ddc->ctx->dc->res_pool->engines[ddc_pin->pin_data->en];
-       if (!acquire(aux_engine, ddc_pin))
+       if (!acquire(aux_engine, ddc_pin)) {
+               *operation_result = AUX_CHANNEL_OPERATION_FAILED_ENGINE_ACQUIRE;
                return -1;
+       }
 
        if (payload->i2c_over_aux)
                aux_req.type = AUX_TRANSACTION_TYPE_I2C;
                        break;
 
                case AUX_CHANNEL_OPERATION_FAILED_HPD_DISCON:
+               case AUX_CHANNEL_OPERATION_FAILED_ENGINE_ACQUIRE:
                case AUX_CHANNEL_OPERATION_FAILED_REASON_UNKNOWN:
                default:
                        goto fail;