Mystery: Security system doesn

[jneely]

Hello, I

[Turbine Doc]

There is a module in the steering column that talks to your PCM if they don't talk it will think you are trying to steal the truck, is it pcm or switch I don't know

go here in the members area to read more about it

http://www.thedieselpage.com/members/duramax/project2-11.htm

you might try to "re-educate" the PCM at dealers with a Tech 2 or the PITA way I'll scan it and see if I can post the PITA way

[Turbine Doc]

Lets see if drag & drop works

DTC P1631 THEFT DETERRENT PASSWORD INCORRECT

Important: While the PCM is in the Auto Learn Procedure, battery voltage must be maintained at all times. This procedure must be followed exactly as indicated or the procedure will have to be repeated from the beginning.


1.. Attempt to start vehicle (vehicle will start and stall) (in my case never got start only crank)'"after the

engine has stalled leave the ignition ON for 10 minutes (security light will remain on for 10 minutes and then

go out).

2. After the Security lamp turns OFF, turn the ignition off 'for 30 seconds.

3, Again, attempt to start vehicle (vehicle will start and stall), (again crank no start for me C-N-S) after the engine has stalled leave the ignition on for 10 minutes (security light will remain on for 10 minutes and then go out).

4. After the security lamp turns OFF, turn the ignition off for 30 seconds.

5. Again, attempt to start vehicle (vehicle will start and stall) , (C-N-S on mine); after engine has stalled leave the ignition on for 10 minutes (security light will remain on for 10 minutes and then go out) or until DTC P1631 sets.

6. Turn the ignition off for 30 seconds.

7. Turn the ignition on wait 30 seconds..

8. Attempt to start the engine.

Does the engine start and operate normally, IF NO: REPEAT # 1-8.
Conditions for clearing the DTC
. A History DTC will clear after forty consecutive Warm - up cycles" If no failures are reported by this or any Other emission related failure.
. PCM battery voltage is interrupted. . Using a scan tool.

[jneely]

Thanks Tim. Those instructions coincide with the typical timing of the system so I guess it resets by itself after a while. The 1999 6.5L GMC Suburban doesn't have the Pass Lock system. There is no resistor on the key so it must be some other type of security in that year. I'd install a bypass if I thought that would fix the problem. The strange thing is that it only seems to happen when I'm in florida on very humid days. Each time I go down there it it rains and is sunny on the same day, the truck Security system won't cycle off. It seems like some part or module is being affeced by the humidity. I'm still wondering...

[Turbine Doc]

Mine 98 has passlock and I believe the 99 does also IIRC all 97+ models have it, nothing in my key either had Walmart make the spare, from what I read in the featured articles post above, the secutity feature is communication between the ignition switch to PCM,

I'm not sure I get how it all works, but my guess it if the switch gets damaged or has to be replaced say like somebody using a slide hammer to pull out the locks cylinder, it stops comms to the PCM and the replacement switch has to be taught to speak to the PCM.

I'd try the theft lock learn it takes about 30 min. Hey the truck won't start now , I don't think trying the learn will hurt anything.

In the post there is also mention of a bypass module you miught want to check into.

Anybody else have an opinion on trying the learn sequence.

J,
After I posted this it got me do doing some thinking; since is this intermittent, sometimes the truck starts normally, I suspect the problem is a wiring connection in either the switch or PCM, also ground connections on these trucks are notoriously bad for intermittents.

Before trying theft lock learn, I'd do a very close inspection of the switch area as that is more prone to motion disturbance, pull switch harness then attempt start to see if you can cause the problem or cure it. A intermittent wire connection would have same result as a thief messing with the lock cylinder.

[ 05-01-2004, 07:13 AM: Message edited by: tbogemirep ]

[More Power]

I haven't played with the security system that uses a resistor in the key, but with Passlock II, I'm real familiar. I took a complete system apart to learn how it functioned, and then reconstructed a new system that would function in the current Project truck. It's still functional - on demand, and I did not wind up using the aftermarket bypass module I bought as a learning aid.

If your system uses a resistor in the key, I suspect the sensor or whatever reads the key is flakey. The ignition modules are pretty pricey..., but you can permanently bypass the system - if you wish to expose your vehicle to a higher level of risk.

There's loads of info on the net concerning "bypass modules" and GM's vehicle theft deterent systems. In the research I did, I learned that about 2/3 of the info you'll find is either questionable or outright wrong. But, there's enough correct info to point you in the right direction.

MP