What are the functions and testing methods of Relay Boxes in vehicle electrical systems on Volkswagen Passat?

The vehicle has a number of electrical accessories that use relays to transmit electrical signals to the components including the fuel injection system, horns, starter, and the fog lamps. Relays are controlled by a low-current control circuit to open and close a high-current power circuit and when a relay is faulty, the power component it operates will not work. Relays are mostly found in the under-dash fuse/relay box and these can be taken out and either tested or replaced as a unit in case of a suspected faulty relay. The relays in question are typically known as the ISO relays, and its numbered terminals reflect the general connection and purpose in the circuit. The relay control circuit has two terminals, one of which is connected to the coil of the relay, and the other to the power circuit. Energized, the coil produces a magnetic field which has the effect of closing the larger contacts of a power circuit supplying power to the loads in the circuit. The control circuit is usually considered to be terminal 85 and terminal 86 and certain connections are necessary when a diode or resistor is involved. Terminal 30 goes to the battery voltage source to be loaded into the circuit and terminal 87 is connected to the ground side of the circuit. An ohmmeter may be used to test the continuity through the relay control coil, to ensure that there are appropriate resistance values in either direction. Also, continuity is not to be existent between terminal 30 and 87 under the de-energizing condition of the relay. The functionality can be verified by hooking jumper wires to the corresponding terminals and ensuring that there is continuity between the power circuit terminals. When the relay passes all these tests, it is a good relay but fails to pass any of them, then it is replaced.

Genuine Volkswagen Passat Relay Boxes

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10 Relay Boxes found

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Volkswagen Passat Fuse & Relay Box Part Number: 5C0-937-125-A
$49.91 MSRP: $69.33
You Save: $19.42 (29%)
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Product Specifications
- Other Name: Plate
- Warranty: This genuine part is guaranteed by Volkswagen's factory warranty.
Fits the following Vehicles:
- 2016-2017 Volkswagen Passat | SE, SEL Premium | 6 Cyl 3.6 L GAS
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Volkswagen Passat Fuse & Relay Box Part Number: 5C0-937-125-C
$79.72 MSRP: $111.65
You Save: $31.93 (29%)
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Product Specifications
- Other Name: Plate
- Warranty: This genuine part is guaranteed by Volkswagen's factory warranty.
Fits the following Vehicles:
- 2014-2022 Volkswagen Passat | Limited Edition, R-Line, S, SE, SE R-Line, SEL, SEL Premium, Sport, TDI SE, TDI SEL Premium, Wolfsburg Edition | 4 Cyl 1.8 L GAS, 4 Cyl 2.0 L DIESEL, 4 Cyl 2.0 L GAS
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Volkswagen Passat Fuse & Relay Box Part Number: 5C0-937-819-E
$229.66 MSRP: $321.65
You Save: $91.99 (29%)
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Product Specifications
- Other Name: Plate
- Warranty: This genuine part is guaranteed by Volkswagen's factory warranty.
Fits the following Vehicles:
- 2012-2015 Volkswagen Passat | SE, SEL Premium | 6 Cyl 3.6 L GAS
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Volkswagen Passat Fuse & Relay Box Part Number: 8L0-941-822-A
$297.68 MSRP: $406.67
You Save: $108.99 (27%)
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Product Specifications
- Other Name: Plate; Fuse Box Main
- Warranty: This genuine part is guaranteed by Volkswagen's factory warranty.
Fits the following Vehicles:
- 1998-2005 Volkswagen Passat | 4 Motion, GL, GL TDI, GLS, GLS 4 Motion, GLS TDI, GLX, GLX 4 Motion, W8 | 4 Cyl 1.8 L GAS, 4 Cyl 2.0 L DIESEL, 6 Cyl 2.8 L GAS, 8 Cyl 4.0 L GAS
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Volkswagen Passat Fuse & Relay Box Part Number: 3C0-937-548
$390.39 MSRP: $533.33
You Save: $142.94 (27%)
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Product Specifications
- Other Name: Fuse Socket
- Warranty: This genuine part is guaranteed by Volkswagen's factory warranty.
Fits the following Vehicles:
- 2006-2010 Volkswagen Passat | 2.0T, 3.6, Komfort, Lux, Turbo, Value Edition, VR6, Wolfsburg Edition | 4 Cyl 2.0 L GAS, 6 Cyl 3.6 L GAS
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Volkswagen Passat Fuse & Relay Box Part Number: 1K0-937-124-K
$408.69 MSRP: $558.32
You Save: $149.63 (27%)
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Product Specifications
- Other Name: Plate; Relay Fuse Plate
- Warranty: This genuine part is guaranteed by Volkswagen's factory warranty.
Fits the following Vehicles:
- 2006-2010 Volkswagen Passat | 2.0T, Komfort, Lux, Turbo, Value Edition, Wolfsburg Edition | 4 Cyl 2.0 L GAS
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Volkswagen Passat Control Module Part Number: 5K0-937-087-AL-ZAN
$502.57 MSRP: $686.57
You Save: $184.00 (27%)
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Product Specifications
- Other Name: Control Unit; Control Module
- Warranty: This genuine part is guaranteed by Volkswagen's factory warranty.
Fits the following Vehicles:
- 2017-2018 Volkswagen Passat | GT, R-Line, S, SE, SEL Premium | 4 Cyl 1.8 L GAS, 4 Cyl 2.0 L GAS, 6 Cyl 3.6 L GAS
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Volkswagen Passat Fuse & Relay Box Part Number: 1K0-937-124-Q
$454.44 MSRP: $620.82
You Save: $166.38 (27%)
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Product Specifications
- Other Name: Plate; Relay Fuse Plate
- Replaces: 1K0-937-124-N
- Warranty: This genuine part is guaranteed by Volkswagen's factory warranty.
Fits the following Vehicles:
- 2006-2008 Volkswagen Passat | 3.6, VR6 | 6 Cyl 3.6 L GAS
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Volkswagen Passat Fuse & Relay Box Part Number: 5C0-937-819-L
$457.49 MSRP: $624.98
You Save: $167.49 (27%)
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Product Specifications
- Other Name: Plate
- Replaces: 5C0-937-819-B
- Warranty: This genuine part is guaranteed by Volkswagen's factory warranty.
Fits the following Vehicles:
- 2012-2014 Volkswagen Passat | TDI SE, TDI SEL, TDI SEL Premium | 4 Cyl 2.0 L DIESEL
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Volkswagen Passat Fuse & Relay Box Part Number: 5C0-937-819-Q
$457.49 MSRP: $624.98
You Save: $167.49 (27%)
Ships in 1-2 Business Days
ADD TO CART
Product Specifications
- Other Name: Plate; Relay Fuse Plate
- Replaces: 5C0-937-819-H
- Warranty: This genuine part is guaranteed by Volkswagen's factory warranty.
Fits the following Vehicles:
- 2012-2014 Volkswagen Passat | S, SE, SEL, SEL Premium, Wolfsburg Edition | 5 Cyl 2.5 L GAS

Volkswagen Passat Relay Boxes

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Volkswagen Passat Relay Boxes Parts and Q&A

Fuse & Relay Box
8L0-941-822-A
Q: What are the functions and testing methods of Relay Boxes in vehicle electrical systems on Volkswagen Passat?
A:
The vehicle has a number of electrical accessories that use relays to transmit electrical signals to the components including the fuel injection system, Horns, starter, and the fog lamps. Relays are controlled by a low-current control circuit to open and close a high-current power circuit and when a relay is faulty, the power component it operates will not work. Relays are mostly found in the under-dash fuse/relay box and these can be taken out and either tested or replaced as a unit in case of a suspected faulty relay. The relays in question are typically known as the ISO relays, and its numbered terminals reflect the general connection and purpose in the circuit. The relay control circuit has two terminals, one of which is connected to the coil of the relay, and the other to the power circuit. Energized, the coil produces a magnetic field which has the effect of closing the larger contacts of a power circuit supplying power to the loads in the circuit. The control circuit is usually considered to be terminal 85 and terminal 86 and certain connections are necessary when a diode or resistor is involved. Terminal 30 goes to the battery voltage source to be loaded into the circuit and terminal 87 is connected to the ground side of the circuit. An ohmmeter may be used to test the continuity through the relay control coil, to ensure that there are appropriate resistance values in either direction. Also, continuity is not to be existent between terminal 30 and 87 under the de-energizing condition of the relay. The functionality can be verified by hooking jumper wires to the corresponding terminals and ensuring that there is continuity between the power circuit terminals. When the relay passes all these tests, it is a good relay but fails to pass any of them, then it is replaced.