For the last several months, if I unlock the truck using the key (not the plip), the red alarm indicator light continues to flash. The alarm does not sound, but when I try to start the truck the starter does not turn over. All the instrument panel indicators light up for the bulb check. I can start the truck only after I press the unlock button on the plip. It makes no difference whether I have locked the truck with the key or with the plip.

After this sequence, the UltraGauge indicates a pending trouble code – P1668. The Hawkeye shows “P1668 Anti-Theft Alarm System BCU/BeCM Serial Link Timeout Maximum Value Exceeded. Fault NOT Present and Intermittent.”

The RAVE description for P1668 is “Engine anti-theft signal circuit high; Serial link open circuit,” but the RAVE gives no indication of how to address the fault.

There’s a TSB from 2001 pasted in a DiscoWeb post from 2005 (and elsewhere) that states the only remedy is to replace the BCU, or send the BCU to LRNA to be reprogrammed. The TSB says specifically that even TestBook can’t correct the problem.

The good news is that I now have a second plip as insurance, thanks to keninnc renting the Nanocom from Brandon318, but I would nonetheless prefer to be able to unlock and start the truck with the key only. I would hate to have this triggered and be one of the owners who don’t have a plip at all.

It’s possible I triggered the problem while playing around with some of the security settings via the Hawkeye. There are two settings in the Security module in the Hawkeye that seem relevant, but they don’t appear to be the problem – “Alarm Disarm - ALWAYS DISARM WITH KEY,” and “Passive - NO PASSIVE IMMOBILIZATION.”

There are several posts on various forums that include references to P1668, but the TSB from DiscoWeb seems on-point the most.

What I don’t know is whether or not anyone has found a workaround or fix in the 19 years since the TSB was published. I’d also like to know if anyone else on this forum has encountered this condition with their truck.

Lemme know, please. Thanks.

 

just sent you a DM. having same issue after plugging in nanocom.

 

I had that code a few years ago, same thing, starter didn't turn, all indicators on. Read the UG, saw the code, Cleared the code, Started right up. Never happened again, not sure what I did but assume it was some accidental pushing of fob buttons.

 

I've seen that code pop up when the battery is getting low as well. The guys at Nanocom told me once that if you're connecting the Nanocom up for any extended period of time it was a good idea to have the D2 battery hooked up to a trickle charger. Same rule applies to most cars while having firmware updates applied. It must be hooked up to a battery charger to keep the voltage high enough for the ECU's to be happy and not crash during an update or reprogramming.

 

I'm confident the battery has been topped up through these episodes.

Quite a while back a forum member here bought a Nanocom. We used it to set up a second keyless entry fob for my truck, and then we poked around in some of the other settings (set the EKA code, etc.). It may be that some other security setting got changed that's causing this problem. I doubt that's what happened, but I plan to connect his Nanocom one of these days when it's convenient for both of us to look through the settings and see if anything jumps out. I looked through the security settings accessible using my Hawkeye but found nothing.

 

thanks everyone for weighing in! @mln01 are you thinking trickle charge the battery and/or code reset?

 

You can check out the Nanocom and the settings at their website. They have an Emulator that gives a simulation of what it looks like to connect the Nanocom to the D2

https://www.nanocom-diagnostics.com/

There does not seem to be a security setting to change this.

My D2 does the same thing. If I lock the door with the physical key or fob it remains immobilized if I unlock the door with only the physical key.

My guess is the BCM does not have the ability to know if the D2 was locked by the physical key and therefore only a physical key unlock is does not get the OK to to turn off the immobilizer. Therefor it needs the fob to be pressed to let the BCM to know to turn off the immobilizer.

 

And to follow up on my last post. Passive immobilization is disabled on my D2.

Passive immobilization if enabled would turn the immobilization back on after the door is unlocked with the fob but the engine is not started within a set amount of time. This would not change the immobilizer being turned off with the first unlocking of the door.

 

What's weird about this condition is that I used to be able to lock, unlock and start the truck with a plain key.

This behavior cropped up only in the last year or so. I don't drive the truck much these days so I don't recall for certain whether or not it started immediately after the Nanocom session. Plus, we know there are several owners who have a plain key only, and have no keyless entry fob, yet they can lock, unlock and start their trucks.

 

Can I ask a really dumb question? Why are you unlocking the truck with the key anyway if the remote works? If there a reason... ? This might help troubleshoot. (I ask bc it's a bit abnormal, the plip is somewhat easier, arguably)

Re: Nanocom -- Pretty sure there is a setting in Alarm...in BCU. I think this is it:Alarm disarm:
This setting programs the effect that usage of the vehicles key has on disarming the alarm system. Options:

 Operation of the key in the drivers door can always disarms the vehicle (ALWAYS).
 Key only Operation of the key in the drivers door only disarms the vehicle if it was locked with the key (KEY ONLY).
 The security system is not disarmed by the key (except via an EKA) (KEY NEVER).

That TSB is about passive immobilization, which the other poster is right ... it would activate if say you waited 30 seconds or so. Yours seems to do it immediately.

Either way, it could just be a bad BCU.