My anti theft light does not flash when I lock the car

Tiny
DAVE32Z
  • MEMBER
  • 2005 JEEP GRAND CHEROKEE
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 85,000 MILES
The anti lock system isn't starting when I lock the car with my key fob.
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Monday, December 28th, 2020 AT 1:53 PM

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Tiny
CARADIODOC
  • EXPERT
Using a scanner is the easiest way to see why the anti-theft system isn't arming. Most commonly the hood or a door isn't fully-closed, or its switch is defective. The scanner will list every related switch and its state, meaning "open" or "closed".

Another real good suspect is a broken or frayed wire between the door hinges. That can result in the computer failing to see that door is locked. On many models, that harness can be unbolted at each end, then unplugged, to make it easier to repair on a workbench. If yours doesn't unplug, I'll describe for you how I handled these on the older Caravans.
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Monday, December 28th, 2020 AT 7:20 PM
Tiny
DAVE32Z
  • MEMBER
All doors lock and unlock okay, headlights go on when locked for proper time car horn beeps when doors are locking. This is a Jeep not a Caravan I have a OBD2 scanner will that show the problem.
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Tuesday, December 29th, 2020 AT 9:34 AM
Tiny
CARADIODOC
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My reference to Caravans is if you have the same design wire harness between the door hinges as Caravans use. About 99 percent of cars and light trucks use the same design. A few Jeep models use a different, more user-friendly design that allows you to do the repairs on a workbench instead of while squished between the door and body. At the dealership, one of my specialties was electrical, so I did this wiring repair on a half dozen Caravans. I came up with a simple twist to the repair that would make it take half as long if it ever needed to be done again in the distant future. That is what I will describe if it applies to your Jeep.

I never did this repair on Jeep models. The few that came in for this repair were done by other available techs so I could stay busy on the alignment rack. I watched the people doing this repair to learn from their experiences, so I can only describe the procedure from what I observed.

Proper operation of the power door locks is not a valid clue. There's two wires running into each door for its lock motor. Those have nothing to do with the anti-theft system. When the vehicle has the optional factory-installed anti-theft system, there will be an additional switch inside each door, tied to the lock mechanism. On older models, that was a separate switch bolted to the door, and attached to the lock cylinder with a linkage that could accidentally pop apart. Even though the door locked with the power lock motor, a disconnected switch would still tell the computer the door was unlocked. That would prevent the anti-theft system from arming. The same false information would show up if one of that switch's wires was broken between the door hinges.

On most newer models, that switch is built into the latch assembly. Ford in particular has had a lot of problems with these switches, but it can happen on any vehicle. With most other brands and models, the wires cause many more problems than the switches themselves.

As for the scanner, OBD2, (On-board diagnostics, version 2) emissions system refers to the engine and drive train systems. That system was required on '96 and newer models so you have the right scanner. I have a Chrysler DRB3 for all of my older vehicles. If I plug in an additional card, it will work all the way back to '83 models, but its main use was for '96 and newer models. The first year it was obsolete was for 2004 Dakotas and Durangos. Every year after that it worked on fewer and fewer models. The last year it worked was for a few 2008 Jeep models. By 2009, every model needed the newer scanner model. Based on that, it's pretty likely an OBD2 scanner is what is needed for your model, but it depends on the type of scanner you have.

There are some rather effective, inexpensive aftermarket scanners that will only work with Engine Computers. I've used a few of them and found them to be extremely slow in updating displayed data, but you do get the information you need. In the past, if you spent less than around $100.00 for the tool, it likely only accessed Engine Computers, and the $30.00 units only read out diagnostic fault codes. Those are simple code readers. True scanners are "bi-directional", meaning it will take information from a computer and display it for you to read, and you can talk back to the computers and command them to do things like turn relays on and off so the circuits can be tested.

Today there are some fairly useful scanners for as little as $100.00, but they never do as much as dealership-level scanners. Specifically, yours needs to access the "RKE", (remote keyless entry), module and the Body Computer. In the drop-down menu, select "Inputs / Outputs", then, if there's another drop-down menu, select "Switch State". In one of those there will display a long list of all the switches monitored by those computers, and it will show their "state". My DRB3 lists them as "Pressed" or "Released" to avoid confusion. The idea is to look at each one while you activate that switch and see if it changes state properly.

I haven't used my scanners for the anti-theft system very often, so my memory might be a bit fuzzy. There are separate sections for "Engine crank / no-start", "Cruise control inoperative", and I think a similar one for "Anti-theft failure to arm". These screens show only the data relative to that problem. For example, all the steering wheel switches for the cruise control are shown for the cruise control problem, and it might show that a switch is constantly being pressed, when in fact, it is stuck and you aren't even touching it. This is where you'd have to view the data and recognize what is not normal or correct.

If your scanner doesn't have the ability to access the computers for the anti-theft system, you'll need to find a mechanic with one that can. For my newer 2014 Ram, I have a Snapon Solus Edge updated to 2018 models. Snapon is real proud of their annual updates, and they charge accordingly for them, as in around $1000.00 per year. To add to the insult, if you want to update it to current models, you can't skip any years. You have to buy, for example, the 2015 update for $1,000.00, before you can buy the 2016 update, ... Before you can buy the 2017 update, and on and on. A brand new model only costs around $4,000.00, (plus a lot extra for Asian imports, and again for European imports), so instead of paying the high cost of updates every year, a lot of shops just buy a new one every five or six years, or they have just one current model and let their others become outdated. For that reason, you can find a lot of these on eBay for as little as $700.00. There's a lot of them updated to only 2012 or 2014 models, but those will work fine for your Jeep. You can get a really good deal as long as you won't need it for models newer than what it's updated to. This model comes real close to doing everything the dealerships' scanners do, plus it has additional aids to help with diagnosing most problems. It includes flow charts or lists of steps in diagnosing the causes of most diagnostic fault codes, and in some cases it will display common solutions to problems.

If your scanner accesses the RKE and Body Computers, start with that. If it doesn't, start by pulling the rubber boot back to inspect the wires between the driver's door hinges.
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Tuesday, December 29th, 2020 AT 1:15 PM
Tiny
DAVE32Z
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That's a lot of good info. My car was 1 year old when I got it and still was under warrantee so I used it to go to our condo in Mexico so I bought ended buying the OBD2 when It was about 3-4 years old for about $200.00 plus. I have only used it a couple of times and it was a lot of help then. I have noticed that the alarm has not armed last sprig when I returned from our winter snowbird trip and found that the people that stored the car had put the battery back into the car to move it and left it in for about 5 months. So when I went to start it it hardly turned over and I had to jump start it with another battery that was barely able to turn it over. Eventually I had to get a battery pack to get it running. Could it be that the computer needs to be rebooted? If so how do I do that? Is there a fuse that runs the alarm system or just runs via the computer?
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Tuesday, December 29th, 2020 AT 2:54 PM
Tiny
CARADIODOC
  • EXPERT
To share some information from one of the Chrysler schools I attended years ago, "Chrysler says a good, fully-charged battery will crank an engine fast enough to start after sitting for three weeks". Today that is the industry standard except when specified differently by the manufacturer. That is due to the drain from the memory circuits in the many computers. Personally, I've made it as much as six weeks for my '93 Dynasty that's always in storage, but that's not expected. To achieve that three weeks, the acceptable battery drain is limited to 35 milliamps, (.035 amps). Cadillac is one notable exception that allows up to 50 milliamps.

For future reference, there is always a way to stop that battery drain when the vehicle is going to be stored. In the late '80s, that was a large wire right behind the battery that had a single bullet connector. Later that became the "IOD", (ignition off-draw) fuse, usually a ten-amp fuse. Removing that would kill things like signals and radio, but it kept enough systems working to allow haulers to deliver vehicles to the dealership. Part of the New-Vehicle Prep included pounding on wheel covers, screwing on antenna, checking lug nuts, and popping the IOD fuse in.

By 2005, the IOD fuse was no longer labeled as such. Since it included the Air Bag Computer in its circuit, today the two air bag fuses get pulled out to kill the current drain. Anything bright yellow is related to the supplemental restraint, (air bag) system. Therefore, you'll find two fuses inside a bright yellow fuse holder, and plugged into the fuse box. They're also identified that way for safety responders to disable the system after a crash. In this case they're inside the Integrated Power Module under the hood.

Removing these fuses is considered normal, so no special procedures are needed when they're plugged back in. The same would result when the battery is disconnected or run dead. What I have found with my Dynasty, is when I pop a battery in it, the anti-theft system turns on with flashing lights, but not the horn. I have to have a key ready to lock and unlock a front door to disarm the system.

There's no other way to disable the alarm system permanently. If that could be done, car thieves could do it too.
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Tuesday, December 29th, 2020 AT 5:18 PM

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