phil068

I have a 2000 coupe and 2 years ago had issues with the security light coming on and intermitent starting. I replaced the key and ignition cylinder and that fixed both problems. Since putting it back on the road this spring I started to have the no start problem more frequently than ever (to the point of sometimes not starting for an entire day) and the security light coming on. I figured the cylinder was gone again,so I did the VATS bypass with a resistor the exact same resistance as my pellet and that did not fix the problem, still had intermitent starts. I did the 30 min Vats relearn procedure and the cars started right up with the security light off. After a day the security light would sometimes be on and sometimes off but ignored it as the car was starting and working fine. It has been fine for about a month but this morning I went to go to work, and no start with security light flashing. I dont understand how this can be since I have the resistor installed. I didnt have time to pull codes as I was late for work, will do it when I get home. Has anyone had a similar issue? Really starting to get frustrated. Any sugestions would be appreciated. Thanks

Bill Curlee

Please read and post your DTCs. That will help us figure it out. If there are a ton of them, clear them and see what comes back

READING YOUR Engine Diagnostic Codes



The Diagnostic Display Mode is entered with the following procedure:
1) Turn on the ignition but don't start the engine.
2) Press the RESET button to turn off any warning messages. (i.e. door open, trunk open ect)
3) Press and hold OPTIONS
4) While holding OPTIONS, press FUEL four times within a 10-second period.


Initially, on-board diagnostics go into an Automatic Mode which shows diagnostic codes in a pre-set sequence: PCM - TCS - RTD - BCM - IPC - RADIO - HVAC - LDCM - RDCM - SCM - RFA. All codes will be displayed for each. ( i.e. PCM = 4 codes) If none are present in a given module, you will see No More Codes on the display.
There are two kinds of diagnostic codes, Current and History designated with a letter suffix, “C” or “H”. A current C code indicates a malfunction is present and active in the module displaying data. A history code indicates a problem existed sometime in the last 40 or 50 ignition cycles. When not accompanied by a current code of the same number, it's potential evidence of a previous problem, now resolved, that was not removed by clearing the codes.
More likely it's an indication of an intermittent malfunction.
Intermittent codes are the most challenging of the diagnostics. An intermittent code may have happened once, may have happened more than once but is inconsistent or may be happening on a regular basis but not at the time the codes are displayed. History codes can also be caused by a current malfunction in a system that is not operating at the time codes are displayed. An example is the rear window defogger which doesn't operate until the Body Control Module detects engine rpm. For history codes set by a module that does not operate with the key on and engine off, a special diagnostic tool called a Scan Tester is necessary to properly diagnose the malfunction.
Once the system has displayed all modules, it goes into the manual mode which allows selection of each module using combinations of Driver Information Center buttons. Manual mode can also be entered during the automatic sequence by pressing any button except English/Metric (E/M). Once the display shows Manual Diagnostics, select a module by pressing the OPTIONS button to go forward or the TRIP button to go back. Once a module is selected, a code is displayed, and if more than one are present; press GAGES to go forward or FUEL to go back.
To exit the diagnostic mode at any time, press E/M. If you want to erase codes in a given module, press and hold the RESET button To reset the codes once in manual mode, press and hold RESET until it displays NO CODES Press OPTIONS to go to the next module. Repeat the steps until you have reset the codes in all the computer modules.
NOTE!! Only reset the codes IF you want to - it is NOT necessary to do this. Clearing a code does not repair a problem. You are simply erasing the evidence of it in the module's memory. If you clear the code/s, and extinguish the Check Engine Light, your emissions status ready will NOT allow you to pass an emissions test until you have completed the required driving cycles.
Once you have the codes, the next question is: What to do with the information?
First, consult the factory service manual. Any serious C5 Do-It-Yourself owner should invest in the Corvette Service Manual of the appropriate model year. The Service Manual is really a requirement if you want to understand and work on your C5. You can GOOGLE the DTC and also find information on it.




Here is very good site that explains the DTCs:


http://www.corvette-web-central.com/C5DTCcode.html


http://www.obd-codes.com/trouble_cod...d-ii-codes.php



Make sure to include the H or C suffix!!

lucky131969

Pull the codes. The problem is compounded because you have the resistor installed. At this point, there is no telling if you have an additional problem, or your bypass is suspect. I would remove the bypass, and troubleshoot the issue in a "stocK" configuration......or you may just continue chasing your tail.

phil068

Now home from work i have pulled the codes. It all seems to point to a bcm problem. The codes I am getting are P1631HC, B2578H,B2721HC.I am sure this has nothing to due with the bypass as the resistor is the exact same resistance as the key and it is installed properly. These are all bcm codes, sounds like my bcm is having issues and am contimplating replacing it. Any other less expensive ideas?

Bill Curlee

YES! Disconnect the battery, remove the BCM, remove the circuit board from the aluminum box and carefully inspect for ANY corrosion. Look around and UNDER relays and other components. If there is any, remove it with alcohol and a soft acid brush.

The board is ESD (static) sensitive.

If you need a new one, Gene Culley www.gmpartshouse.com for the best price. There expensive.

BC

BC

Bill Curlee

You still have some sort of security issue;

DTC P1631
Circuit Description
The powertrain control module (PCM) controls the fuel injector operation and the starter operation based on a vehicle theft deterrent (VTD) password from the vehicle body control module (BCM). When the ignition is first turned ON, the BCM sends a programmed theft deterrent password to the PCM. The PCM acknowledges the password and responds to the BCM that normal fuel injector and starter operation will continue. If the PCM detects an incorrect password, a theft deterrent system failure, or an attempted vehicle theft, DTC 1631 will set. The engine will not start or crank as long as the condition is present.

Conditions for Running the DTC
The ignition is ON.

Conditions for Setting the DTC
The PCM detects an incorrect password from the VTD system.
The condition is present for less than 1 second.
Action Taken When the DTC Sets
The body control module (BCM) send a class to message to the instrument panel cluster (IPC) to illuminate the SECURITY indicator.
The PCM will not illuminate the malfunction indicator lamp (MIL).
The PCM will store conditions which were present when the DTC set as Failure Records data only. This information will not be stored as Freeze Frame data.
Conditions for Clearing the MIL/DTC
A History DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
The DTC can be cleared by using a scan tool.
Diagnostic Aids
DTC P1631 indicates that the vehicle theft deterrent password that the PCM has learned does not agree with the password received from the VTD system. This condition can occur if an incorrect key is used when attempting to start the vehicle, or if the BCM has been replaced and the PCM Password Learn function has not been enabled. If the BCM has been replaced, the password must be relearned.

Step
Action
Yes
No

1
Did you perform the Theft Deterrent Diagnostic System Check?
Go to Step 2
Go to Diagnostic System Check - Theft Deterrent

2
Is DTC B2721, B2722, B2723 or B2735 set as a current code?
Go to Diagnostic Trouble Code (DTC) List
Go to Step 3

3
Perform the Programming Theft Deterrent System Components procedure. Refer to Programming Theft Deterrent System Components .

Did you complete the action?
Go to Step 4
--

4
Use the scan tool in order to clear the DTCs.
Operate the vehicle within the conditions for Running the DTC as specified in the supporting text.
Does the DTC reset?
Go to Step 2
System OK

DTC B2721
Circuit Description
The body control module (BCM) supplies a 5 volt signal and a ground circuit for the PASS-Key® system. This allows the BCM to detect PASS-Key® resistance values. Inserting the PASS-Key® (with resistor pellet) in the ignition lock cylinder completes the PASS-Key® circuit. Contacts in the ignition lock cylinder mate with the pellet contacts. The BCM compares the resistance value of the key pellet to the valid resistance programmed into the BCM. If the proper resistance value is read, the BCM allows the following functions to occur:

The theft deterrent relay to energize.
The steering column to unlock.
The BCM sends a message through the serial data line to the powertrain control module (PCM) to enable fuel delivery.
If the resistance value is incorrect, a malfunction is present and a DTC will set.

Conditions for Setting the DTC
The resistance level sampled at the BCMs PASS-Key® signal circuit is one of 15 valid but incorrect resistance ranges, signaling an invalid PASS-Key® detection.
This condition must be present for 1 second.
Action Taken When the DTC Sets
The BCM stores DTC B2721 in memory.
The BCM sends a message to the instrument panel cluster (IPC) to illuminate the SECURITY indicator.
The BCM will disable the theft deterrent relay.
The PCM will not allow fuel delivery to occur.
The BCM disables sampling of the PASS-Key® resistance for a time-out period of 3 minutes.
The steering column remains in the locked position.
Conditions for Clearing the DTC
This DTC requires an ignition cycle in order to change from current to history.
The BCM detects a valid PASS-Key® resistance value on the PASS-Key® signal circuit after the 3 minute time-out period occurs.
A history DTC will clear after 50 consecutive ignition cycles if the condition for the malfunction is no longer present.
Use the IPC clearing DTCs feature.
Use a scan tool.
Diagnostic Aids
The following conditions may cause an intermittent malfunction:
There is an intermittent open or short to ground on the PASS-Key® signal or ground circuit.
There are poor connections at the BCM or the ignition switch connector.
The ignition lock cylinder key contacts or the PASS-Key® resistor is dirty or loose.
If the key resistor pellet is incorrect, there will be no BCM outputs to the theft deterrent relay or to the PCM. This state will last about 3 minutes. If a key is inserted, or the ignition is turned ON again before the 3 minute time frame is complete, the timer will reset to 3 minutes. Disconnecting the battery will not clear the timer sequence, but the timer will reset to 3 minutes when the battery power is restored. Even if a proper key is inserted during one of the time periods, the vehicle will not start until the total time period has elapsed.
Test Description
The numbers below refer to the step numbers on the diagnostic table.

Tests for other PASS-Key® DTCs stored in the BCM that will cause a DTC B2721 to set. These DTCs must be diagnosed first.

Tests for an intermittent or incorrect PASS-Key® Resister reading due to an incorrect or malfunctioning ignition key.

Step
Action
Yes
No

Schematic Reference: Theft Deterrent System Schematics

Connector End View Reference: Theft Deterrent System Connector End Views

1
Did you perform the Theft Deterrent Diagnostic System Check?
Go to Step 2
Go to Diagnostic System Check - Theft Deterrent

2
Install a scan tool.
Turn ON the ignition with the engine OFF.
Select the Display DTCs function for the BCM.
Does the scan tool display DTC B2721 as a current DTC?
Go to Step 3
Go to Testing for Intermittent and Poor Connections in Wiring Systems

3
Does the scan tool display DTC B2722 or B2723 as a current DTC?
Go to Diagnostic Trouble Code (DTC) List
Go to Step 4

4
Inspect the ignition key for dirt or obvious damage.

Does the ignition key appear dirty or damaged?
Go to Step 11
Go to Step 5

5
Turn OFF the ignition.
Disconnect the ignition lock cylinder.
Connect a J 35628-A Vats/Passkey Interrogator using terminal adapters from a J 35616-A to the key resistor input circuit and key resistor reference ground circuit.
Turn the rotary switch on the J 35628-A to each code number (1-15) and attempt to start the vehicle with each code number. (After each failed starting attempt, you must wait 3 minutes before the next attempt. This step may take as long as 45 minutes due to a trial and error process.)
Does the vehicle start with one of the codes selected on the J 35628-A ?
Go to Step 6
Go to Step 7

6
Note the code number on the J 35628-A that successfully started the vehicle.
Obtain and cut a new ignition key with the correct key code value.
Attempt to start the vehicle with the new ignition key.
Does the vehicle start?
Go to Step 13
Go to Step 8

7
Test the following circuits for an open or a short:

The key resistor input circuit
The key resistor reference ground circuit
Did you find and correct the condition?
Go to Step 13
Go to Step 9

8
Inspect for poor connections at the harness connector of the ignition lock cylinder. Refer to Testing for Intermittent and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?
Go to Step 13
Go to Step 11

9
Inspect for poor connections at the harness connector of the body control module. Refer to Testing for Intermittent and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?
Go to Step 13
Go to Step 12

10
Clean or replace the ignition key as necessary. Refer to Replacing Keys .

Did you complete the procedure?
Go to Step 13
--

11
Replace the ignition lock cylinder. Refer to Ignition Switch Lock Cylinder Replacement in Instrument Panel, Gages, and Console.

Did you complete the replacement?
Go to Step 13
--

12

Important
When replacing the BCM, perform the relearn procedure. Refer to Body Control Module (BCM) Programming/RPO Configuration in Body Control System.


Replace the BCM. Refer to Body Control Module Replacement in Body Control System.

Did you complete the repair?
Go to Step 13
--

13
Use the scan tool in order to clear the DTCs.
Attempt to start the vehicle.
Does the DTC reset?
Go to Step 2
System OK



--------------------------------------------------------------------------------
Document ID# 679684
2003 Chevrolet Corvette

phil068

I didnt have time to pull the bcm as it was getting dark. I plan on doing that this weekend. I did the 30 min relearn procedure and the car started right up and the security light is now off. Exactly the same as when I did this about a month ago. One thig I did find that worries me is right above the bcm there is three wires that were cut and taped. The three wire are orange , black, and yellow. They come out of the wiring harness to a factory conector, then on the other side of the connector they are cut. cant seem to find where they were cut from. Any idea what these wires are for? I dont think this is related to the current problem as these wires must have been like that since I bought the car almost 4 yrs ago. I am the only one who has ever worked on the car and I didnt cut them. As for the bcm, I'll disassemble it this weekend and let you know what I find.

lucky131969

Factory wiring for adding accessories. The ends should be taped.

phil068

Heres the update. I pulled the BCM and opened the case. everything looked fine, no water marks or corrosion. I reinstalled it, did the 30 min relearn, then cleared the codes. Drove the car around a bit last night, no secutiry light and every time I stopped the car checked the codes and all was clear. Driving around doing errands to today and back on comes the security light. The car is still starting fine, but I think it is a matter of time before I get stuck again and have to sit there for 30 min and do the relearn, which seem to be the only that fixes it. I pulled the codes and I am getting 2721hc. I have been having the same issue with the light coming on weather I have the vats connected , or the resistor pypass. So it has to be something to due with the communication between the pcm and the bcm. That is why the relearn seems to always fix it. Does the pcm ever have problems? From what I have read seems like the bcm can quite often be the culprit. Just hate to spend big money on a bcm without knowing for sure if that is the problem.