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Porsche 928: Why Does My Alarm Keep Going Off?

Click here to learn the best DIY tricks around for fixing a malfunctioning car alarm system in the Porsche 928.

By Tom Cavanagh - April 13, 2015

This article applies to the Porsche 928 (1979-1995).

While car alarm systems provide a trusted sense of safety and security, especially when parking your vehicle in an unfamiliar area or curbside, an alarm that sounds without stopping can be a real hassle and create unnecessary feelings of panic and distress. Fortunately, there are a number of ways of going about fixing this problem. Let's get started with the most obvious culprits before introducing other common scenarios that might be causing or exacerbating the problem.

Material Needed

  • Door key (not ignition key)

Step 1 – Disable the alarm from inside the cabin

Doing so manually could be the answer to your problem.

Unlock the door to your 928 using the key. This will disable the alarm and immediately stop the system from sounding.

Figure 1. The longer key is the one you will need.

Pro Tip

You must use your key. The inside release will not work.

Step 2 – Inspect the hatch lock

It might be damaged and triggering the alarm as you drive.

To do this, you'll need to pull back the trim where the hatch lock is located and inspect the wiring and connectors for damage. Telltale signs of serious damage include visible signs of corrosion, general wear and tear, fraying, and other physical damage. If you notice any distress to the wiring and connectors, then hire a professional mechanic to fix the problem, or, if you prefer, you could purchase a replacement (new or used) and have it "keyed in."

Figure 2. Physical damage most likely points to an alarm system that is "busted."

Pro Tip

Even one offending wire could impair the entire system. If minor dirt is visible, clean the switches and backs of the locks to see if this fixes the problem.

Step 3 – Jumper the alarm module

The circuit may be "open." You will need to troubleshoot the relay board to fix the problem.

Construct a female-ended jumper wire, and then set it aside while you complete the following modifications. Unplug the "Z" plug, which is located at the center bottom portion of the CE panel just beneath the three red wires that plug into the panel. Press a piece of tape down over the "Z" plug. Hide the plug away. Link terminal "Z1" with "Z6" using the jumper you just constructed. Now, seated in the passenger seat (facing toward the exposed male terminals on the panel up ahead), the pattern is as follows:

Z3 Z6

Z2 Z5

Z1 Z4

Figure 3. This is alarm system 928 up to model 83.
Figure 4. This is a jumper that was constructed for this step.

Step 4 – Visit a local garage

Seek the help of a professional mechanic if the above-mentioned steps do not resolve the problem. The system control in your 928 might have "aged out" and become faulty. In this case, you would need a replacement, which should be installed by a professional to avoid costly damage to your vehicle.

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