Rick's Free Auto Repair Advice » Alarms and Anti-Theft Systems

A/C doesn’t work and ABS light on

Rick — Thu, 01 Sep 2011 17:53:39 +0000

GM vehicles are known for faulty ignition switches. The problems are almost always intermittent. One common symptom is for the A/C to start blowing warm air or for the blower fan to stop (depending on which GM model we’re talking about), along with an ABS light. The problem is usually the ignition switch heating up and not providing power to the A/C clutch and the ABS computer. If you want to diagnose the problem, buy a wiring diagram for your vehicle form eautorepair.net or alldata.com (there are way to many GM models to list their wiring diagrams here) and test for power at the switched terminals when the problem happens. Or, just replace the ignition switch.

For more information on this repair or any others for your vehicle, buy an online subscription to either Alldatadiy.com or eautorepair.net. Click on this link to compare the two services: Compare Alldata and Eautorepair.

If you just need information for a single repair and want to save money,eautorepair offers a lower price 1-week subscription for only $11.99. Or, if you’ll be working on this vehicle in the future, you can buy a 1-year subscription (Alldatadiy.com for $26.99, or eautorepair.net $29.99)

Alldatadiy.com

eautorepair.net

Both Alldata and Eautorepair offer professional grade shop manuals at a price you can afford. Check them out!.

Passlock – How it works

Rick — Sun, 13 Sep 2009 03:29:24 +0000

The Passlock anti-theft system disables the engine unless you have inserted the proper key. The diagram shown here is for vehicles with a steering column mounted ignition cylinder. Late model GM vehicles may have a dash mounted cylinder, but the system is similar. In late model vehicles, GM move the theft logic to the Body Control Module instead of the instrument panel cluster.

There are 3 main components to the system:

1) Passlock lock cylinder (R)
2) Powertrain Control Module (PCM)
3) Instrument Panel Cluster (IPC) or Body Control Module (BCM)

When you insert a key into the lock cylinder and turn it, the cylinder rotates a magnet past a stationary sensor to create a signal. The signal, referred to as a “Resistance Code” (R-code) is sent to the IPC (BCM in later GM vehicles). The IPC contains a computer, stored R value, logic, and data transmission circuitry. If the IPC determines that the R-code is correct, it sends an encoded password to the PCM. The PCM allows the fuel injectors to operate.

The R-code must be read by the IPC within a preset time period or the Vehicle Theft Deterrent (VTD) system will begin “Short Tamper Mode.” When Short Tamper mode kicks in, the engine will run for about 4 seconds and the “THEFT” light will flash. Then the PCM will cut off the injectors and the engine will quit. The user can attempt to start the vehicle a total of 3 times before the system goes into Long Tamper Mode. During Long Tamper, the PCM will shut off the injectors for 10 minutes and flash the THEFT light. The user may be able to crank the engine, but it will stall due to fuel starvation.

The most common failure points on this system are the IPC and the lock actuator (housing the magnet and sensor).

The IPC or BCM provides 5 volts to the sensor on the white wire and ground on the black wire. Start your diagnostics by checking for power and ground on these wires. Then check the voltage on the yellow wire while turning the key. It should go down as you turn the key. If it does not, replace the sensor. Repeat the key-turn procedure and continue to check that the voltage drops to the SAME value with each key turn. If it does not, replace the sensor.

RELEARN Procedure.

If you replace the IPC or BCM, you must perform a relearn procedure.
1) Try to start the vehicle. If it runs and quits, go to step #2. If it continues
to run, make sure the THEFT light turns off after 10 seconds. If the light stays on, there is another problem with the system.

2) The THEFT light should be flashing. Leave the ignition switch in the RUN
position until the THEFT light glows solid (10 minutes—stick around and use your watch to time this). Turn the key to OFF. Then try to start the vehicle again. It should now operate.

Some companies make PASSLOCK OVERRIDE SYSTEMS. I don’t have any experience with them. But if you want more information, click HERE

Alldatadiy.com

eautorepair.net

Both Alldata and Eautorepair offer professional grade shop manuals at a price you can afford. Check them out!.

Hover your mouse over the REPAIR ARTICLES tab at the top of the page. The click on DIAGNOSTICS to search by SYMPTOM, TROUBLE CODE, or read TECH TIPS on how to diagnose a problem

Click on MAKE an MODEL to see all the articles I’ve written for your vehicle
Click on REPAIR TOPICS to read individual articles written for specific automotive systems

If you’ve had your car scanned and know the trouble code go to TROUBLE CODES

Here are some quick links to speed up your research

Click on the link below for speedy navigation:

ABS issues, how to bleed ABS brakes

Airbag issues or SRS light on

Alternator issues or how to test

Belt diagram or serpentine belt issues

Blower motor

Blower motor resistor

Brakes, brake issues, what kind of brake parts to buy, ABS issues

Car Alarms or Antitheft systems

Cooling system, Water pump, What type of coolant to use

Engine flush

Firing order, cylinder layout, finding #1 cylinder

MAF or MAP sensor

Oxygen sensors, How they work, How to change, How to test

PassLock or Passkey

Thermostat issues

Transmission flush

Serpentine belt diagrams

Window issues, power window motor, replace window regulator, glass adhesive

Anti-Theft Systems for GM Vehicles

Rick — Fri, 29 May 2009 16:33:00 +0000

GM has used a variety of anti-theft systems on their vehicles. When you get a no start, intermittent start, or start then die, you should diagnose the anti-theft system before you start replacing starting components. A tell-tale sign that you’ve got an anti-theft problem is a flashing “Theft” light. Here’s a brief primer on each system and what to look for.

Each GM anti-theft system disables different components. Some disable the engine starter, while others enable the starter but disable fuel injectors. None of them disable spark. So, first understand the difference between vehicle theft deterrent systems.

VAT
The VAT, or vehicle anti-theft was used primarily on 1986-88 Corvettes. The key had a pellet that was married to the vehicle anti-theft module at the factory. If the lock cylinder was turned or bypassed with the proper key installed, the system would disable the starter and kill the injectors. You could NOT perform a system “relearn.”

PassKey I, and II
Similar to the VATS system, these vehicles also used a pellet key. You can identify this system by looking at the key. It has a black resistor pellet with a thin metal edge running along the key. The system enables the starter, but shuts down the injectors after initial startup. So the vehicle would start, then die. This system has a “relearn” feature. It was used on these vehicles

Buick
Century 97-01
Park Avenue 91-96
LeSabre 92-99
Riviera/Reatta 90-01
Regal 94-99
Roadmaster 94-96

Cadillac
Eldorado 89-01
Seville 89-97
Fleetwood 92-96
Deville 90-99
Allante 89-93

Chevrolet
Camero 89-01
Corvette 89-01
Caprice/Impala 94-96
Lumina/Monte Carlo 95-97

Oldsmobile
Cutlass Supreme 94-97
Aurora 95-00
Regency/88 91-99
Toronado 90-93
Pontiac
Firebird 89-01
Grand Prix 94-96
Bonneville 92-99

PassKey III
This system uses a special key (PK3 stamped on the shoulder of the key) with a transponder under the rubber cover. The receiver module is located next to the lock cylinder. When the key is positioned next to the lock cylinder receiver module, it energizes the transponder which sends a coded signal to the receiver. The receiver module checks its memory to see if the signal is correct. If it is, the module sends a signal to the PCM to enable the engine. If the value is valid, the indicator light will remain steady for 2 seconds. You cannot test this system with an ohmmeter. You need a scan tool. If the signal is not correct, the PCM disables the injector and the starter and flashes the light once per second. If an illegitimate key is used or a system problem exists, the light flashes twice per second.

The system is used on:

Buick
Lesabre 2000-on
Park Avenue 97-on

Cadillac
Seville 98-on
Deville 2000-on

Oldsmobile
Aurora 01-on

Pontiac
Bonneville 2000-on

GM Minivans
Venture, Montana, Silhouette

Passlock
This system allows starter operation, then kills the injectors 1-2 seconds after startup. This is a “Hall-Effect” system. The key cylinder housing has a small magnet that rotates past the Passlock sensor. The sensor is powered and detects the rotation. The voltage on the sensor then drops to a specified value (there are 10 different values). There’s no pellet in the key. So basically this system is checking to see that a thief has not popped the lock cylinder to steal the vehicle. you have to perform a Powertrain Control Module (PCM) relearn procedure (need a programming scan tool). The Passlock system was used on:

Buick
Skylark 96-98

Chevrolet
Cavalier 95-on
Impala 2000-on
Malibu 97-on
Monte Carlo 2000-on

Oldsmobile
Achieva 96-on
Cutlass 97-on
Intrigue 98-on

All GM trucks 98-0n

SYSTEM DIAGNOSTICS

PassKey I and II System Diagnostics

There are 15 different key codes. Measure the resistance of the key pellet by connecting an ohmmeter to each side of the key pellet. Once you find the resistance value, remove the lower dash panels and locate two small wires (both white) that run down the base of the steering column. Disconnect the electrical connector where those wires terminate. Then connect an ohmmeter to that electrical connector and insert the key. The reading you get at the end of the two white wires should match the resistance value you got from the key. Next, turn the key. The value on your meter should NOT change or drop out. If it does, you will have to replace the key cylinder. It is COMMON for the wires to break from the key cylinder.

If you have the PassKey system and the engine cranks, runs, and quits AND the THEFT light is on (for about 5 seconds), here are the tests you should perform:

1) Disconnect the electrical connector at the deterrent module. Then turn the ignition switch to RUN while you test the voltage between the dark blue wire in the theft deterrent electrical connector (the one you just disconnected) and a ground point. You should see 5 volts. If you don’t get that voltage, check for an open or short between the dark blue wire and the PCM that supplies the voltage to the module.

If you DO get the 5 volts, turn the ignition off and reconnect the electrical connector. Pierce the insulation on the same wire (with a pin) or back-probe the wire in the connector. Turn the ignition to RUN. The voltage should now read 2.5 volts. If not, replace the theft module. THAT assumes you have already conducted the key pellet test (explained above) and that it passes the test. If you see 2.5 volts and the vehicle still won’t stay running, check the fuel pump relay.

Here’s how it works, The lock cylinder reads the resistance of the pellet in the key and transmits that data to the theft module. Meanwhile, the PCM provides 5 volts on the dark blue wire. When the theft module determines that the proper key has been inserted, it partially grounds the voltage on the dark blue wire. The PCM initially provides fuel injector pulse, but if it doesn’t sees a voltage drop on that dark blue wire, it cuts off the fuel injectors. That’s why you get a crank, start, engine shut down.

So, if the vehicle starts and then dies, AND THE THEFT LIGHT FLASHES, the module is not getting the proper signal from the lock cylinder or the module is bad.

Passlock
Testing this system is similar to the Passkey I and II systems. You want to check the voltage at the bottom of the steering column as you insert the key and rotate it check the yellow signal wire (should be 5 volts before you start the testing). Turn the key.

The value should drop. If it does not, you will have to replace the key cylinder. The “control module” for this system is built into the instrument panel control (IPC) in early years. In later years, the system is controlled by the Body Control Module (BCM), the Electronically Controlled Orifice-steering Assist (EVO), IPC and other systems. If you have to replace the lock cylinder or any of the control modules,

Passkey III

You cannot check this system with an ohmmeter. You will need a scan tool to watch the operation of the system and find the trouble code. Once you get the trouble code, follow the diagnostic procedure based on the specific code.

Some companies make PASSLOCK OVERRIDE SYSTEMS. I don’t have any experience with them. But if you want more information, click HERE

Alldatadiy.com

eautorepair.net

Both Alldata and Eautorepair offer professional grade shop manuals at a price you can afford. Check them out!.

Hover your mouse over the REPAIR ARTICLES tab at the top of the page. The click on DIAGNOSTICS to search by SYMPTOM, TROUBLE CODE, or read TECH TIPS on how to diagnose a problem

Click on MAKE an MODEL to see all the articles I’ve written for your vehicle
Click on REPAIR TOPICS to read individual articles written for specific automotive systems

If you’ve had your car scanned and know the trouble code go to TROUBLE CODES

Here are some quick links to speed up your research

Click on the link below for speedy navigation:

ABS issues, how to bleed ABS brakes

Airbag issues or SRS light on

Alternator issues or how to test

Belt diagram or serpentine belt issues

Blower motor

Blower motor resistor

Brakes, brake issues, what kind of brake parts to buy, ABS issues

Car Alarms or Antitheft systems

Cooling system, Water pump, What type of coolant to use

Engine flush

Firing order, cylinder layout, finding #1 cylinder

MAF or MAP sensor

Oxygen sensors, How they work, How to change, How to test

PassLock or Passkey

Thermostat issues

Transmission flush

Serpentine belt diagrams

Window issues, power window motor, replace window regulator, glass adhesive

GM Passlock–Diagnosing and Fixing GM Anti-theft related no-starts

Rick — Tue, 13 May 2008 03:11:00 +0000

The GM Passlock system is fairly simple, especially when compared to other makes. However, if yours is goofing up, you won’t think it’s so simple.

Here’s how it works: When you first turn the key, the PCM provides power to the fuel pump, injectors, and ignition system. You can crank and start the engine. However, there’s a magnet built into the lock cylinder. As you rotate the key, the magnet passes over a Hall Effect sensor—a sensor that detects the presence of a magnetic force. The magnet produces a unique voltage when it passes over the sensor. The sensor sends this voltage signal to the Body Control Module where it is compared to a stored value. If the sent voltage doesn’t match the stored value, the PCM shuts down the fuel injectors for a minimum of 10 minutes and, well, you’re pretty screwed at that point. If you try to start the car again, you will see a blinking Security light. That’s your sign that the Passlock system has shut you down.

What goes wrong: GM vehicles experience a very high failure rate in the lock cylinder and lock housing mechanisms. Fortunately, they’re fairly inexpensive and easy to replace.

Testing the Passlock sytem: Remove the plastic cover shrouds from the steering column near the lock cylinder. Inside you will see the Passkey module surrounding the lock cylinder. It will have 3 wires coming out of it. Turn the key to the ON position and use a DIGITAL multimeter (Do NOT use an analog meter) to backprobe the probe the black and white wires. If you see 12 volts on the white wire and 0 volts on the black wire, you can proceed to the test for the Passkey module. If you do not see those voltage values, you have a wiring problem between the connector and the BCM.

Next, connect your voltmeter to the yellow wire. It should read 5 volts. Keep the probe connected and turn the key to the off position and back to the start position. The Passlock Data Voltage has a potential of 10 different values, ranging from .86 to 4.28 volts. The voltage should drop to a voltage level between those values and stay within .02 volts of the initial reading for at least one minute. Repeat the test several times—you must receive the same voltage for each test. If you do not, replace the lock cylinder and the Passkey housing.

To remove the lock cylinder, first disconnect the negative battery cable and allow the airbag to power down for 5-10 minutes. Slide the Passkey module off the cylinder housing. Insert the key and turn the lock cylinder to the start position. Place a 1/16” allen wrench into the hole on top of the lock module to release the steering column lock cylinder set pin. Then turn the lock cylinder to the RUN position and pull the lock cylinder out. Reverse the procedure to install.

After you replace the cylinder and Passkey module, you will have to conduct a relearn procedure for the BCM to learn the new voltage value. Here’s the procedure: Lock doors and unlock. Clear codes. Turn key and bump starter, leave on for 10 minutes. After a few minutes the dash light will go out. At that point, turn the key to the off position for 90 seconds to 3 minutes. Repeat this procedure 3 times for a total of 30 minutes and on the 4th try the car will start.

Some companies make PASSLOCK OVERRIDE SYSTEMS. I don’t have any experience with them. But if you want more information, click HERE

Alldatadiy.com

eautorepair.net

Both Alldata and Eautorepair offer professional grade shop manuals at a price you can afford. Check them out!.

Hover your mouse over the REPAIR ARTICLES tab at the top of the page. The click on DIAGNOSTICS to search by SYMPTOM, TROUBLE CODE, or read TECH TIPS on how to diagnose a problem

Click on MAKE an MODEL to see all the articles I’ve written for your vehicle
Click on REPAIR TOPICS to read individual articles written for specific automotive systems

If you’ve had your car scanned and know the trouble code go to TROUBLE CODES

Here are some quick links to speed up your research

Click on the link below for speedy navigation:

ABS issues, how to bleed ABS brakes

Airbag issues or SRS light on

Alternator issues or how to test

Belt diagram or serpentine belt issues

Blower motor

Blower motor resistor

Brakes, brake issues, what kind of brake parts to buy, ABS issues

Car Alarms or Antitheft systems

Cooling system, Water pump, What type of coolant to use

Engine flush

Firing order, cylinder layout, finding #1 cylinder

MAF or MAP sensor

Oxygen sensors, How they work, How to change, How to test

PassLock or Passkey

Thermostat issues

Transmission flush

Serpentine belt diagrams

Window issues, power window motor, replace window regulator, glass adhesive

Theft light on after PCM replacement—GM vehicle

Rick — Tue, 29 Apr 2008 05:42:00 +0000

If you swap out a PCM in a late ‘90’s GM vehicle and encounter an anti-theft light, you may not have to take it to the dealer for reprogramming. The PCM is set up to recognize a certain pattern as it relearns the key code. You can duplicate the pattern by performing this sequence exactly:
1) Hook up a battery charger and set at low rate of charge.
2) Turn the key to crank the engine just long enough to engage the starter.
3) Leave the key in that position for at least 10 minutes. (Some shops say it takes as long as 30 mins).
4) When the theft light turns off, turn the key to OFF for 5 seconds and then back to start and leave key in that position for 10 minutes.
5) When the theft light turns off a second time, the PCM has learned the new key code and you can start the engine.

Some companies make PASSLOCK OVERRIDE SYSTEMS. I don’t have any experience with them. But if you want more information, click HERE

Alldatadiy.com

eautorepair.net

Both Alldata and Eautorepair offer professional grade shop manuals at a price you can afford. Check them out!.

Hover your mouse over the REPAIR ARTICLES tab at the top of the page. The click on DIAGNOSTICS to search by SYMPTOM, TROUBLE CODE, or read TECH TIPS on how to diagnose a problem

Click on MAKE an MODEL to see all the articles I’ve written for your vehicle
Click on REPAIR TOPICS to read individual articles written for specific automotive systems

If you’ve had your car scanned and know the trouble code go to TROUBLE CODES

Here are some quick links to speed up your research

Click on the link below for speedy navigation:

ABS issues, how to bleed ABS brakes

Airbag issues or SRS light on

Alternator issues or how to test

Belt diagram or serpentine belt issues

Blower motor

Blower motor resistor

Brakes, brake issues, what kind of brake parts to buy, ABS issues

Car Alarms or Antitheft systems

Cooling system, Water pump, What type of coolant to use

Engine flush

Firing order, cylinder layout, finding #1 cylinder

MAF or MAP sensor

Oxygen sensors, How they work, How to change, How to test

PassLock or Passkey

Thermostat issues

Transmission flush

Serpentine belt diagrams

Window issues, power window motor, replace window regulator, glass adhesive

Alarm Systems Triggering Misfire Codes

Rick — Tue, 21 Aug 2007 01:02:00 +0000

GM has determined that aftermarket alarm systems that use mechanical relays wired into the ignition system can generate actual ignition misfires that are serious enough to damage the catalytic converter. Mechanical relays have contact points mounted on a spring. Vehicle movement, pot holes, bumps, etc., can jolt the contacts enough to interrupt the ignition circuit for a few milliseconds. That’s enough time to cause a misfire. The unburned fuel from that misfire causes overheating in the catalytic converter and if the misfire continues, can actually cause a meltdown of the precious metals inside the converter.

GM’s research of common aftermarket alarm system found that all used a mechanical relay. The use of a solid state relay could eliminate the problem. Until the alarm manufacturers re-design their system, installers and do it yourself vehicle owners should avoid connecting the alarm system to the ignition circuit. They should instead use the starter circuit.

Buy a new alarm system here

GM has also advised their dealers of this problem and if your car is showing any of these misfire codes, P0300, P1380, or P01381, you should try disconnecting your alarm system before taking the vehicle into the dealer. If the misfire and converter codes continue, then you can at least rule out the alarm system. Otherwise, the dealer may charge you for diagnostics related to your alarm system.

Alldatadiy.com

eautorepair.net

Both Alldata and Eautorepair offer professional grade shop manuals at a price you can afford. Check them out!.

Hover your mouse over the REPAIR ARTICLES tab at the top of the page. The click on DIAGNOSTICS to search by SYMPTOM, TROUBLE CODE, or read TECH TIPS on how to diagnose a problem

Click on MAKE an MODEL to see all the articles I’ve written for your vehicle
Click on REPAIR TOPICS to read individual articles written for specific automotive systems

If you’ve had your car scanned and know the trouble code go to TROUBLE CODES

Here are some quick links to speed up your research

Click on the link below for speedy navigation:

ABS issues, how to bleed ABS brakes

Airbag issues or SRS light on

Alternator issues or how to test

Belt diagram or serpentine belt issues

Blower motor

Blower motor resistor

Brakes, brake issues, what kind of brake parts to buy, ABS issues

Car Alarms or Antitheft systems

Cooling system, Water pump, What type of coolant to use