Jun 182017

1998 Chevy SilveradoSecurity light stays on

The security light stays on and the truck won’t start. New pass lock sensor, ignition switch and computer. I can connect the battery cables together over night then turn the truck over without it starting and wait about twelve minutes and the light goes off. I’ve tried a three hundred dollar bypass that worked when I hooked it up but went back to the same problem.

Assuming the ignition key is good. First thing to check would be the fuses. Check fuse 21 (10 amp). It provides power to the EVO/PASSLOCK™ Module. Then check for battery positive at the RED/WHT wire on the Passlock Sensor. Then check for ground at the Passlock Sensor. Next using a multi-meter test the resistor on the RED/WHT wire. Should see 10 ohms. Use the provided wiring diagram to assist in tracing the wiring harness and connections.

Anti-Theft Wiring Diagram 1998 Chevy 1500

Vehicle Theft Deterrent (VTD) Operation

The design of the passlock™ system is to prevent the vehicle operation if the proper ignition key is not used in order to start the vehicle. A mechanical key, in normal operation, will turn the passlock™ lock cylinder. Then the passlock™ sensor will relay the passlock™ data to theEVO/Passlock™ module. Next the EVO/Passlock™ module will determine the validity of the passlock™ data. The EVO/Passlock™ module will send a code password to the vehicle/powertrain control module (VCM/PCM). When the VCM/PCM receives the correct code the VCM/PCM allows the fuel injectors to operate normally. The passlock™ system requires the VCM and the EVO/Passlock™ module to communicate the various functions in order to operate. These functions transmit over the class 2 serial data line CKT 1807.

Vehicle Theft Deterrent (VTD) Description
Passlock™ System

The design of the passlock™ system is to prevent vehicle theft by disabling the engine unless the passlock™ lock cylinder rotates properly by engaging the correct ignition key. The system is similar in concept to the passkey system. However, the passlock™ eliminates the need for a key mounted resistor pellet. The components of the system are as follows:

  • The ignition lock cylinder
  • Ignition switch
  • The passlock™ sensor
  • EVO/Passlock™ module
  • Security indicator
  • The vehicle/powertrain control module (VCM/PCM)
Ignition Lock Cylinder and Housing

The ignition lock cylinder is located at the upper right side of the steering column. The Passlock™ sensor is in the steering column. The sensor is separate from the key and lock cylinder. The key and the lock cylinder work together in order to determine if the proper ignition key was used to start the vehicle.

In the event of an open Class 2 serial data line between the EVO/Passlock™ Module and the VCM/PCM, the vehicle will become fail-enabled if the VCM/PCM has already received the password from the EVO/Passlock™ Module for that ignition cycle (the engine is running). In this event, the following conditions occur:

  • The security telltale will be ON continuously.
  • The VCM/PCM will become fail-enabled for future ignition cycles.

If a failure in the Class 2 serial data line occurs before the ignition cycle, when the VCM/PCM is not fail-enabled, the following conditions occur:

  • The VCM/PCM will never receive a valid password in order to enable the fuel injectors.
  • The vehicle will not start.
Ignition Switch

The lock cylinder and the visible key insert portion of the ignition switch are located at the upper right side of the steering column. The electrical switching portion of the assembly is separate from the key and lock cylinder. An electrical switch portion is hidden inside the steering column. The electrical switch portion and the key and lock cylinder synchronize and work in conjunction through the action of the mechanical assembly between the 2 parts.

Passlock™ Sensor

The passlock™ sensor is inside the upper right side of the steering column. A passlock™ sensor contains 2 hall effect sensors. The tamper hall effect sensor is on the top. The security hall effect sensor is under the tamper hall effect sensor. Both of the hall effect sensors monitor the magnet of the lock cylinder through an opening. The tamper hall effect sensor is physically placed on top of the security hall effect sensor. This placement enables the tamper hall effect sensor to engage first if an intruder attempts to bypass the passlock™ sensor by placing a large magnet around that area of the steering column. There is a tamper resistor inside the passlock™ sensor in order to help prevent tamper to the system. Passlock™ equipped vehicles have a selection of 10 different security resistors ranging up to 13K ohms. Install any of the security resistors inside the passlock™sensor in order to generate a unique passlock™ code. All 10 combinations of the passlock™ sensor have the same part number. However, you cannot simply replace the passlock™ sensor and expect the system to operate properly. Always start by performing the Diagnostic System Check first and following the instructions.

EVO/Passlock™ Module

The EVO/Passlock™ module contains the theft deterrent system logic. The EVO/Passlock™ module reads the passlock™ data from the passlock™ sensor. If the passlock™ data is correct, the EVO/Passlock™ module will pass theft. The EVO/Passlock™ module will then transmit the code password to the VCM/PCM.

During the tamper mode the vehicle may start. The vehicle will quickly stall. If the EVO/Passlock™ module receives the wrong passlock™ data, the VTD will immediately go into the tamper mode. The tamper mode will lock-out the vehicle fuel injectors for 10 minutes. The SECURITY indicator will flash while the VTD is in the tamper mode.

If the passlock sensor sends a correct password to the EVO/Passlock module when the ignition is in the ON position, the EVO/Passlock module will send a fuel enable signal to the VCM/PCM. The VCM/PCM will not disable the fuel due to any EVO/Passlock module message for the remainder of the ignition cycle.

SECURITY Indicator

The SECURITY indicator is on the instrument cluster.

Vehicle/Powertrain Control Module

The VCM/PCM communicates with the EVO/Passlock Module over the Class 2 serial data line. When the EVO/Passlock™ Module determines a no start condition, it sends a Class 2 serial data password to the VCM/PCM in order to disable the fuel injection system. If the EVO/Passlock™ Module receives the expected voltage from the Passlock™ sensor, the EVO/Passlock™ Module sends a Class 2 serial data password to the VCM/PCM in order to enable the fuel injection system. The VCM/PCM then allows the vehicle to start correctly. If the Class 2 serial data password from the EVO/Passlock™ Module to the VCM/PCM is not within the Vehicle Security Status Message, the fuel injectors will shut OFF during a start attempt. The SECURITY telltale will be ON STEADY for approximately 10 minutes and then turns OFF. If the VCM/PCM does not receive the same password from the EVO/Passlock™ Module as the last learned one, the vehicle will start and quickly stalls due to the Fuel Lockout.

Changing the Passlock™ Components

The design of the passlock™ system is to prevent theft even if the various theft deterrent parts change. The parts that can no longer be changed without the possibility of going into a tamper mode are:

  • The passlock™ sensor
  • The EVO/Passlock™ module
  • The VCM/PCM

If you replace any of these parts the vehicle may start and stall for 10 minutes. This is the long tamper mode. If this occurs, the system must go through a long tamper mode cycle. During this time the SECURITY indicator will be flashing for the full 10 minutes and the DTC B3031 will be set. The EVO/Passlock™ module and the VCM/PCM require the full 10 minutes in order to complete a learn cycle. The ignition switch must remain in the RUN position until the SECURITY indicator stops flashing. You will need to repeat the cycle if the ignition switch does not remain in the RUN position. When replacing any of the above parts it is recommended to perform one of the following procedures:

  • Seed and Key Procedure.
  • Auto Learn Procedure.
Jun 172017

Chevy C1500

No Crank, No Start

My wife parked my truck and now it doesn’t crank. The starter is good. The battery is good. I also changed the ignition switch. I drove it last week and noticed the speedometer was jumping. Now when I hook the battery up the heater is on and the chime goes off without the key in. Some gauges are messed up too. Is my problem the BCM ?

Is the problem the BCM? NO! There is no involvement of the BCM to getting the engine to crank over. Looking over the provided wiring diagram it appears there are a couple of things left to check.

  1. Crank Fuse
  2. Fusible Links
  3. Clutch Start Switch/Neutral Switch
  4. Wiring Harness

How to Diagnose No Crank, No Start

With the use of a multi-meter you may check for battery voltage at the “S” terminal on the starter while someone holds the ignition key in the “START” position. If you see battery positive at the “S” terminal and the starter still does not crank, double check for battery negative on the case of the starter. Repair block ground if no battery negative is seen. If battery negative is seen on the case of the starter and battery positive is seen on the “S” terminal with the ignition key in “START”, Replace the starter.

No battery positive seen on at “S” terminal with ignition in “START” position

Trace wiring from one side of each component in the circuit until you locate the battery positive. Then repair the wiring, the connection or replace the effected component. Since you have made the repair it makes sense to test it again.

Starting Circuit Wiring Diagram 1994 Chevy 1500

Jun 152017

1994 Chevy Blazer

1994 Chevy Blazer 350 wont start

Okay I’ve been dealing with this for a few days and its really eating away at me. I’m sure I’m missing something small. But anyway, I have a 1994 Chevy Blazer, 4×4, 350, with 220k miles. I recently replaced my oil pressure sensor, control module and starter.

Okay, now she wont start. First thing I think the flywheel is worn down to much in one spot. Only in that spot the starter just spins. I have the shims on there but it still makes a god awful noise trying to start. While trying to start the throttle body is spiting out gas.

I did the old paper clip diagnostic and came out with a fuel pump relay low voltage. I also noticed the sending unit above the oil filter is not connected and I can find what connector goes on there the truck has spark I don’t have any gauges to check oil pressure I don’t know what to do.

Wont Start

It sounds like the check engine light code is sending you in the right direction. Try some starting fluid and see if she tries to fire up. If it does then you will want to check the fuel pressure. No fuel pressure would indicate a failure of one of the following:

  1. Fuel Pump Relay
  2. Fuel Pump Inline Fuse
  3. Wiring Harness
  4. Fuel Pump
  5. Leak In Fuel System
Jun 122017

1999 Chevy Camaro Z28

Evaporator core

I need to know how to r+r the ac evaporator core does it come out from inside the car or the outside? If outside do I need to pull engine?

No need to remove the engine or anything drastic like that since the evaporator core comes out from under the passenger side dash.

Evaporator Core Removal

  1. Disconnect the negative battery cable. Discharge the air conditioning system. Remove the right instrument panel sound insulator panel. Take the heater hoses off the heater core after the coolant has been drained. Open glove box. Push sides of glove box in and remove glove box. Remove heater core.
  2. Remove temperature control cable at temperature valve case. Take out the bolts, located in engine compartment, from temperature valve case. Slide temperature valve case down to disengage upper case clip and remove temperature valve case.
  3. Place a mat on the passenger floor to protect carpeting. Using a small hand saw, remove the perforated section of heater and A/C evaporator module as one piece (do not discard). Remove bolts and hoses retaining A/C evaporator. Slide evaporator to left. Remove evaporator from heater and A/C module.

Evaporator core removal diagram

To learn more or to get the complete replacement instructions feel free to grab your vehicle specific auto repair manual.

Jun 032017

 Chevy 25001997 Chevy 2500 5.7 hesitates from thirty miles a hour and up?

Could be a number of things. However if the check engine light is illuminated you will want to start there. Pull the check engine light codes and post them in the comments for further assistance with them.

7 possible causes for engine hesitation

  1. Contaminated fuel
  2. Ignition system issue
  3. Dirty air filter
  4. Clogged catalytic converter
  5. Clogged fuel filter
  6. Spark plugs worn
  7. Spark plug wires/coil over boot

Fuel pump isn’t buzzing 2002 Chevy Tahoe

 Auto Repair Questions, Chevy  Comments Off on Fuel pump isn’t buzzing 2002 Chevy Tahoe
May 232017

Chevy TahoeJust put a fuel pump on 2002 Tahoe. The fuel pump was working when I first put it on but still wouldn’t crank. Now the dash board has went out. Attempting to get started now. When I turn the key, the only thing it shows is a check engine light. But the gauges won’t move, the message board doesn’t light up and the fuel pump isn’t buzzing any more. I need help I’m out of answers

Fuel pump isn’t buzzing

First thing to do would be to make certain the battery is fully charged. A weak battery can lead to confusion during diagnostics from false readings. So, charge the battery or replace it with one that is fully charged before continuing with your diagnostics.

May 192017

Chevy TrailblazerEngine surges under medium acceleration, no mil light. Bad distributor gear?

Surges under medium acceleration

My thought would be more fuel related. Remove the air filter and test. If you see a change then you know it is fuel related. Concentrate on that area. Replace fuel filter, air filter and move to high octane at a different station at the next fill up.