2002 chevy tahoe 5.3 vin z flex fuel no start

2002 chevy tahoe 5.3  vin z flex fuel. Crank no start/ starts but dies right away. I lose injector pulse after it starts. The computer shuts fuel off but there are no codes. Will run with starting fluid

What are you using to determine you are losing injection pulse? Oscilloscope, noid light? Have you checked fuel pressure? If so what is your pressure?

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Does the vehicle theft fuel shut off display yes?

Noid light

I believe my scanner is active and inactive. And it activates while cranking. So yes

  779.207.0557

Loss of injector pulse after 1 - 1 1/2 seconds is a classic symptom of Theft Deterrent Security.

Thanks for the info. Ate there different options cus my key doesn't have a transponder. It's just a plain metal key and it worked before. The wires from the security at the ignition run down to the bcm. I velive thus has a pass lock system off the steering column. How would I go about testing that. I can provide more info or pics as well.

wrote:

Thanks for the info. Ate there different options cus my key doesn't have a transponder. It's just a plain metal key and it worked before. The wires from the security at the ignition run down to the bcm. I velive thus has a pass lock system off the steering column. How would I go about testing that. I can provide more info or pics as well.
 

This is a passlock system. I don't know why Alldata gave the description of a PK3 system.  I should have done a little reading before posting that link. My apologies.

I believe, the BCM supplies the passlock sensor with a 5 voltage bias voltage on the yellow wire.  As the key is turned, the voltage is pulled down.  There are, I think, 10 different voltages that it could be pulled down to. If the voltage is pulled down to the proper voltage, the BCM sends the fuel enable message.  You should be able to read this voltage with a scan tool.  I will try to find the right service info to post.
 

Here is the reset procedure:

30 MINUTE LEARN PROCEDURE
 1. Turn ON the ignition, with the engine OFF.
 2. Attempt to start the engine, then release the key to ON (vehicle will not start).
 3. Observe the SECURITY telltale, after approximately 10 minutes the telltale will turn OFF.
 4. Turn OFF the ignition, and wait 5 seconds.
 5. Repeat steps 1 through 4 two more times for a total of 3 cycles/30 minutes (the vehicle is now ready to relearn the Passlock Sensor Data Code and/or passwords on the next ignition switch transition from OFF to CRANK).

 IMPORTANT: The vehicle learns the Passlock Sensor Data Code and/or password on the next ignition switch transition from OFF to CRANK. You must turn the ignition OFF before attempting to start the vehicle.

Thank you! I've been trying this but I can't get it to learn. How would you go about testing the resistance from the passlock? Would getting a resistance reading from the signal wire to ground be a valid reading? In my case there are 3 wires of the ignition cylinder. Yellow wich I believe it's the signal from the passlock to the bcm, orange and black with is ground referenc and red n white with is battery voltage. If getting resistance reading from the signal wire is an accurate way then I'm only getting OL

 

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How would you go about testing the resistance from the passlock? Would getting a resistance reading from the signal wire to ground be a valid reading?

 

Hmm. I'm not sure.  I suppose, if you were to measure current flow of the signal, you could apply Ohm's Law.

Let's back up a bit, though.  When you first try to start the truck, and it dies after 1 - 1 1/2 seconds. Then  you, immediately try to start it again. Does it start die, again? Or, does it just crank?  Anti-theft will lock out the injectors for 10 minutes. Any attempts to start, after the first start/stall, will result in a crank, no-start for the next 10 minutes.

What does the security light do? Does it come on, and go out. Does it come on and stay on? Does it flash?

Does  your scan tool have access to  the BCM? There should be a pid for the passlock signal voltage  (yellow wire). Key on-Engine off. Voltage should be 5 volts. When you turn the key to that CRANK position, and release it, the voltage should drop. This voltage drop is what the BCM is "learning" when you do a security relearn/reset. You can, also, back-probe the yellow wire. Report back with what voltages you have on the yellow signal wire.

 

The resistance is switched by a hall effect sensor when the key is turned to crank. So no easy way to measure it directly. And even if you did measure it you'd have no way of knowing if it was correct. Passlock sensor should pull the 5V signal down to somewhere between 0.86-4.28 volts in crank depending on what resistor is installed in it.

Ok, it does not pull it down it stays at 5.16 volts.

It's starts back up it doesn't go into the 10 minute lockout mode. I can start it back up for 1 sec. After a couple seconds. The security light is not on but in the scan tool it says it comes on then Goes off. I noticed that the 5v signal never drops after turning the key.

No codes and not locking out the injectors for 10 minutes makes me think that it is more than a security issue. However, if you have no voltage drop on the yellow 5 volt signal wire, then you DO have a security issue. Are you testing the voltage at the sensor, or the BCM? If you are checking at the BCM, you need to go check at the sensor. Make sure you have a good power and ground at the sensor, too.  If you have good power and ground, then the 5 volt signal should drop when the key is turned to the start position. If it doesn't you need a new sensor. 

If you have access to a labscope, take a look at pin #2 at the DLC. This is the Class 2 Serial Data bus. There should be a 7 to 0 volt toggle, as information is transferred.

Does your scan tool access the BCM?


This is a last ditch effort. I don't, really, recommend this fix. But, it IS a fix:

If the problem is truly a security issue, you can get a bypass module at New Rockies .  I used to install these, before I learned how to diagnose.  This module completely bypasses the security, and sends the Fuel Enable "password" to the PCM, itself.  If the problem is security, this will fix it. If the problem is something else, it will be a waste of money.

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 I noticed that the 5v signal never drops after turning the key.
 

The signal itself is only pulled down while the key is in crank.The Passlock Data Voltage PID "latches" at the value measured in crank when the key returns to run.

Ok thanks guys for the help. So mu conclusion is the passlock sensor is faulty since it's not causing the voltage to drop since I have ground and voltage on the other wires. Also, l found this video about how there are 2 modes for the lock out 1 for 10 minutes and another for 4 seconds.

This is the link explaining the difference of the short and long fuel disable.

The primary difference between Short Tamper mode and Long Tamper mode is the  reset procedure. You can tell that you are in Short Tamper mode by the SECURITY light flashing for 4 seconds, then remaining on. The reset  procedure for Short Tamper only takes 10 minutes...Turn the key on, but do not try to crank the starter. After 10 minutes, the security light will go out. Key off, for 5 seconds. Then, start the vehicle.