diff --git a/openapi.yaml b/openapi.yaml
index 531df490..772ace90 100644
--- a/openapi.yaml
+++ b/openapi.yaml
@@ -7462,7 +7462,7 @@ paths:
           application/json:
             schema:
               type: object
-              required: [reg, type, wash_subscription]
+              required: [reg, type]
               properties:
                 reg:
                   type: string
@@ -7474,6 +7474,8 @@ paths:
                   description: Product ID representing the vehicle wash type
                 wash_subscription:
                   type: boolean
+                  default: false
+                  description: Defaults to false when omitted.
                 reference:
                   type: string
                   maxLength: 255
diff --git a/services/nginx/app/openapi.yaml b/services/nginx/app/openapi.yaml
index 17065f33..77e222e6 100644
--- a/services/nginx/app/openapi.yaml
+++ b/services/nginx/app/openapi.yaml
@@ -7462,7 +7462,7 @@ paths:
           application/json:
             schema:
               type: object
-              required: [reg, type, wash_subscription]
+              required: [reg, type]
               properties:
                 reg:
                   type: string
@@ -7474,6 +7474,8 @@ paths:
                   description: Product ID representing the vehicle wash type
                 wash_subscription:
                   type: boolean
+                  default: false
+                  description: Defaults to false when omitted.
                 reference:
                   type: string
                   maxLength: 255
diff --git a/services/nginx/app/routes/vehiclesRoute.php b/services/nginx/app/routes/vehiclesRoute.php
index e897fb1e..10ea2caa 100644
--- a/services/nginx/app/routes/vehiclesRoute.php
+++ b/services/nginx/app/routes/vehiclesRoute.php
@@ -132,7 +132,6 @@ class vehiclesRoute
             self::requireParameters([
                 'type',
                 'reg',
-                'wash_subscription',
             ]);
 
             // Determine target customer
@@ -165,11 +164,14 @@ class vehiclesRoute
             // Validate the parameters
             self::requireType(self::getParameter('reg'), self::type_string());
             self::requireType(self::getParameter('type'), self::type_int());
-            self::requireType(self::getParameter('wash_subscription'), self::type_bool());
+            $subscription = false;
+            if (self::isParametersSet(['wash_subscription'])) {
+                self::requireType(self::getParameter('wash_subscription'), self::type_bool());
+                $subscription = (bool)self::getParameter('wash_subscription');
+            }
             // Get the parameters
             $reg = (string)self::getParameter('reg');
             $type = (int)self::getParameter('type');
-            $subscription = (bool)self::getParameter('wash_subscription');
             $reg = trim($reg);
 
             // Create a new vehicle
diff --git a/services/nginx/app/tests/Api/VehiclesApiTest.php b/services/nginx/app/tests/Api/VehiclesApiTest.php
index 2298e39f..b113823a 100644
--- a/services/nginx/app/tests/Api/VehiclesApiTest.php
+++ b/services/nginx/app/tests/Api/VehiclesApiTest.php
@@ -4,6 +4,106 @@ declare(strict_types=1);
 
 usesApiSuite();
 
+it('defaults wash subscriptions to false when a customer creates a vehicle without the field', function (): void {
+    api_test_covers('POST /vehicles', 'happy');
+
+    $session = api_fixtures()->createUserSession(['add_vehicle']);
+
+    $response = api_client()->post('/vehicles', [
+        'type' => 53,
+        'reg' => 'DEFAULTOWN',
+    ], $session['headers']);
+
+    $response
+        ->assertStatus(200)
+        ->assertEnvelope()
+        ->assertSuccess();
+
+    $vehicleId = (int)($response->data()['id'] ?? 0);
+    expect($vehicleId)->toBeGreaterThan(0);
+
+    $row = api_fixtures()->fetchRowById('customer_vehicles', $vehicleId);
+    expect($row)->not->toBeNull();
+    expect((int)$row['customer_id'])->toBe((int)$session['user']['customer_number']);
+    expect((int)$row['wash_subscription'])->toBe(0);
+    expect($response->data())->toMatchArray([
+        'id' => $vehicleId,
+        'customer_id' => (int)$session['user']['customer_number'],
+        'reg' => 'DEFAULTOWN',
+        'wash_subscription' => false,
+    ]);
+
+    api_fixtures()->cleanupDeleteById('customer_vehicles', $vehicleId);
+    api_fixtures()->cleanupDeleteWhere('customer_vehicle_subscription_versions', ['vehicle_id' => $vehicleId]);
+});
+
+it('defaults wash subscriptions to false when a superuser creates a vehicle for another customer without the field', function (): void {
+    api_test_covers('POST /vehicles', 'happy');
+
+    $targetCustomer = api_fixtures()->createUser(['display_name' => 'Vehicle Default Target Customer']);
+    $session = api_fixtures()->createUserSession(['add_vehicle_other']);
+
+    $response = api_client()->post('/vehicles', [
+        'customer_id' => $targetCustomer['customer_number'],
+        'type' => 53,
+        'reg' => 'DEFAULTSU',
+    ], $session['headers']);
+
+    $response
+        ->assertStatus(200)
+        ->assertEnvelope()
+        ->assertSuccess();
+
+    $vehicleId = (int)($response->data()['id'] ?? 0);
+    expect($vehicleId)->toBeGreaterThan(0);
+
+    $row = api_fixtures()->fetchRowById('customer_vehicles', $vehicleId);
+    expect($row)->not->toBeNull();
+    expect((int)$row['customer_id'])->toBe((int)$targetCustomer['customer_number']);
+    expect((int)$row['wash_subscription'])->toBe(0);
+    expect($response->data())->toMatchArray([
+        'id' => $vehicleId,
+        'customer_id' => (int)$targetCustomer['customer_number'],
+        'reg' => 'DEFAULTSU',
+        'wash_subscription' => false,
+    ]);
+
+    api_fixtures()->cleanupDeleteById('customer_vehicles', $vehicleId);
+    api_fixtures()->cleanupDeleteWhere('customer_vehicle_subscription_versions', ['vehicle_id' => $vehicleId]);
+});
+
+it('still honors an explicit wash subscription true value on vehicle create', function (): void {
+    api_test_covers('POST /vehicles', 'happy');
+
+    $session = api_fixtures()->createUserSession(['add_vehicle']);
+
+    $response = api_client()->post('/vehicles', [
+        'type' => 53,
+        'reg' => 'EXPLICITON',
+        'wash_subscription' => true,
+    ], $session['headers']);
+
+    $response
+        ->assertStatus(200)
+        ->assertEnvelope()
+        ->assertSuccess();
+
+    $vehicleId = (int)($response->data()['id'] ?? 0);
+    expect($vehicleId)->toBeGreaterThan(0);
+
+    $row = api_fixtures()->fetchRowById('customer_vehicles', $vehicleId);
+    expect($row)->not->toBeNull();
+    expect((int)$row['wash_subscription'])->toBe(1);
+    expect($response->data())->toMatchArray([
+        'id' => $vehicleId,
+        'reg' => 'EXPLICITON',
+        'wash_subscription' => true,
+    ]);
+
+    api_fixtures()->cleanupDeleteById('customer_vehicles', $vehicleId);
+    api_fixtures()->cleanupDeleteWhere('customer_vehicle_subscription_versions', ['vehicle_id' => $vehicleId]);
+});
+
 it('returns the newest vehicle last_order_id that still has order items', function (): void {
     api_test_covers('GET /vehicles', 'happy');