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2001 Jeep Cherokee XJ P1685 Error: Faulty Sentry Key, Immobilizer Module or Aftermarket Alarm?

Model: Cherokee XJ Fault Code: P1685 Posted: 2006-10-04 06:20

I'm experiencing a P1685 error on my 2001 Jeep Cherokee XJ. I want to understand whether this code is caused by a faulty sentry key, a defective immobilizer module, or an aftermarket anti-theft system (such as a GT car alarm). The issue began after installing an alarm system one month following my September 2023 purchase of the vehicle. When the error occurs, the five-bell chime does not sound when turning the key — a behavior I noticed during troubleshooting. The vehicle starts normally under normal conditions, but it fails to start after being parked for several days (e.g., during a vacation). In one instance, after 7 days of parking, the car wouldn't start and the sentry key LED lit up. After towing it to a nearby Chrysler- Jeep dealer (100 km away), the vehicle started again — though the mechanic reported that they had to order a new immobilizer module. However, the actual fix was a loose wiring connection behind the right headlight, costing €120. The issue returned two weeks later when I was at home; after towing it again, the car started once more. I'm concerned about whether this is a recurring issue due to poor installation or a deeper factory component failure. As someone who works at a Jeep dealership, I know that the first step in diagnosing such codes is typically removing aftermarket systems — as 90% of similar issues stem from improper wiring or interference with factory security modules. Could you advise whether my situation points more toward a faulty key, an immobilizer module issue, or an aftermarket alarm system? I’ve tested another key (which works), and the vehicle only responds to one key. What steps should I take next?

Related fault codes

P1685

Comments (11)

Anonymous 2006-10-04 08:41

How long has your theft system been in the vehicle?

Anonymous 2006-10-04 08:52

I purchased this Jeep second-hand in September 2023. The alarm was installed one month later, and the P1685 error began around that time. I'm unsure if it was already present before purchase or if it started after installation.

Anonymous 2006-10-04 11:21

I forgot to mention: when the P1685 error occurs, the five-bell chime does not sound when turning the ignition key.

Anonymous 2006-10-04 11:53

This is likely not a coincidence. Does your Jeep start normally? I’d recommend first removing any aftermarket security systems before blaming factory components. As a Jeep dealer technician, we always begin by disconnecting third-party alarm systems — they are responsible for about 90% of such issues, either directly or through interference.

Anonymous 2006-10-04 12:41

The vehicle starts under normal conditions, but during a vacation it failed to start after being parked for seven days. The sentry key LED lit up. After towing the car to a Chrysler- Jeep dealer (100 km away), it started again. The mechanic said they had to order a new immobilizer module, but the actual fix was a loose wiring connection behind the right headlight — costing €120. Two weeks later, I experienced the same issue at home; after towing it again and having it serviced, it started once more. I'm frustrated because these so-called 'experienced' mechanics overseas seem to overlook basic wiring checks.

Anonymous 2006-10-04 15:40

What year is your Jeep? What color is the key? Is it grey? Have you tried using a different key? What does 'cycling the door locks' mean?

Anonymous 2006-10-05 00:03

The vehicle is a 2001 model. The key is grey. I have tested another key — it works. Could you clarify what 'cycling the door locks' means?

Anonymous 2006-10-05 05:51

Does the alternate key work properly?

Anonymous 2006-10-05 06:46

Yes, the other key functions correctly.

Anonymous 2006-10-05 08:33

If only one key works, then your second key is likely faulty. If that’s not the case, proceed by removing all aftermarket security systems and restoring the vehicle to factory settings before investigating potential issues with the immobilizer module itself.

Anonymous 2006-10-05 10:09

Thank you for your detailed input — I’ll update this thread once I’ve completed the diagnostics or received a resolution. Cheers!