Experiencing a no-start condition with your 2007 Golf Gti can be frustrating. Diagnosing electrical issues, especially within the starting system, often requires a methodical approach. This investigation focuses on a potential problem with the starter relay and unusual voltage readings that are preventing a 2007 Golf GTI from starting. Let’s delve into the troubleshooting steps taken to pinpoint the fault in this starting system.
Initial Voltage Checks at Relay J682 (Power Supply Relay)
The first step in diagnosing this 2007 Golf GTI starting problem involved examining the J682 Power Supply Relay, also known as relay A2 or R2. This relay is crucial for sending power to the starter. By accessing the fuse box and locating the J682 relay, voltage measurements were taken at its terminals with the ignition in the “ON” position (engine not started).
The relay has four terminals, two small (86 and 85) for the control circuit and two large (87 and 30) for the power circuit. A functional test of the relay was performed by applying 12V across terminals 86 and 85, confirming that the relay clicked, indicating it could close the 87/30 circuit.
Voltage readings at the fuse box connectors for the relay were then recorded relative to the battery ground:
- Terminal 86: 12V
- Terminal 85: 3.4V
- Terminal 30: 12V
- Terminal 87: 0V
Terminals 30 and 87 readings are as expected, with 30 constantly powered and 87 open (0V) when the relay is not activated. However, the readings at the control terminals (86 and 85) present a puzzle.
Discrepancies with Wiring Diagram & Unexpected Voltages
According to standard wiring diagrams for a 2007 Golf GTI starting system, terminal 86 should ideally be at 0V with the ignition in the “ON” position. It should only receive 12V when the ignition is turned to the “START” position and the clutch is depressed. The measured 12V at terminal 86 in the “ON” position is unexpected.
Furthermore, terminal 85 should theoretically go directly to ground, indicating a 0V reading. The 3.4V reading at terminal 85 suggests a potential issue within the ground circuit or a voltage leak somewhere in the system.
Attempting to start the 2007 Golf GTI by depressing the clutch and turning the ignition to “START” made no difference to any of these voltage readings. This lack of change further complicates the diagnosis.
Starter Terminal 50 Test & Resistance Mystery
To further isolate the issue, a direct power test was performed. 12V was applied directly to the female terminal “87” in the fuse box. This terminal is connected via a red wire to terminal 50 on the starter solenoid. The expectation was that applying 12V here would engage the starter motor. However, nothing happened.
Next, the resistance from female terminal 87 to battery ground was measured with the battery positive disconnected. Using a multimeter, a resistance of 300 ohms on the Rx10 scale and 10,000 ohms on the Rx1000 scale was observed. This high resistance was unexpected and remains unexplained.
The terminal 50 connector on the starter solenoid was disconnected to investigate further, but measuring resistance from the plug back to terminal 87 proved difficult due to connector access. Resistance measurement directly at terminal 50 on the starter solenoid to ground was considered but postponed due to the existing anomalies.
Ground Point Location & Further Questions
The 3.4V reading at terminal 85 is particularly perplexing, as wiring diagrams indicate this terminal should be directly connected to ground. The diagram suggests terminal 85 should connect to ground “389,” described as “Ground Connection 24 (in main wiring harness).” The precise physical location of this ground point in a 2007 Golf GTI is currently unknown and crucial for further diagnosis.
The presence of 12V at terminal 86 in the “ON” position also needs to be explained. Why isn’t it at 0V as expected? And why does turning the ignition key to “START” not alter any of the measured voltages?
In summary, key questions remain:
- Location of Ground Point 389: Where is ground point “389” physically located on a 2007 Golf GTI? A diagram detailing ground point locations is needed.
- Voltage Explanation: What could explain the 3.4V at terminal 85 and the 12V at terminal 86 in the “ON” position?
- High Resistance from 87 to Ground: What is the cause of the unexpectedly high resistance measured from terminal 87 to ground? Could this indicate a fault beyond just the starter relay itself?
Any insights or assistance in answering these questions would be greatly appreciated as the troubleshooting process continues to resolve this 2007 Golf GTI no-start issue.
