Tech Stuff

Push Button Start Technology

Figure 1: Remember the 1959 Dodge Royal with its push button transmission selector?
<p>Figure 1: Remember the 1959 Dodge Royal with its push button transmission selector?</p>

I’m sure you’ve heard the phrase, “Don’t get pushy.” Well, in the automotive world this phrase seems to have taken on a new meaning. In the last 10 to 15 years or so the number of buttons on a motor vehicle seems to have grown immensely. I remember back in the early days of my automotive career there were fewer buttons to push on the dash and more levers or sliding cable-operated controls than there are on today’s vehicles.

I remember I had a 1959 Dodge Royal which had a push button selector control for the automatic transmission (see Figure 1).

Some vehicles still use a push button style transmission shift selector like the selector found in some of the Allison transmission-equipped trucks on the road today (see Figure 2).

In this article, I want to focus on the advent of the push to start systems on the newer vehicles that are on the road. Push to start or keyless start systems have been in the automobile for quite some time now. Sometimes they are also called smart key systems.

A smart key is an electronic access and authorization system that is available either as standard equipment or as an option in several car models. It was first developed by Siemens in 1995 and introduced by Mercedes-Benz under the name “Key-less Go” in 1998 on the W220 S-Class.

Figure 2: Some vehicles still use a push button style transmission shift selector as found on some Allison transmission equipped trucks.
<p>Figure 2: Some vehicles still use a push button style transmission shift selector as found on some Allison transmission equipped trucks.</p>

Many car manufacturers have adopted the keyless start system due to many reasons. One main reason is there is less mechanical movement involved which will create less wear and tear. Another reason, of course, is the cost factor.

But in today’s market, a major influence in push button start systems is due to the security of both the operator and the vehicle itself. Gone are the days of just obtaining a copy of the key to gain entry. The security systems in these new vehicles are a lot more sophisticated. The average car thief will have a hard time trying to steal the vehicle.

Here’s a quick look at a modern push button start vehicle that will eventually end up in your service bay. This vehicle is a 2019 Chevrolet Traverse. It has a 2.0L turbo-charged engine. This vehicle comes equipped with the start stop system (see Figure 3).

Figure 3: The 2019 Chevy Traverse is equipped with the start-stop system.
<p>Figure 3: The 2019 Chevy Traverse is equipped with the start-stop system.</p>

System diagnostics

Let’s take a look at this system a little closer and see how it works and some of the diagnostics involved with servicing it.

Figure 4: When the vehicle is in the off mode, both LEDs will be off.
<p>Figure 4: When the vehicle is in the off mode, both LEDs will be off.</p>

The ignition mode switch has two LEDs that indicate the vehicle power mode. When the vehicle is in the off mode, both LEDs will be off (see Figure 4). Momentarily pressing the ignition mode switch button once (brake pedal not applied), will enter the vehicle into accessory mode and the amber LED (ACC) will illuminate (see Figure 5).

Figure 5: Momentarily pressing the ignition mode switch button once will enter the accessory mode and the amber light will illuminate.
<p>Figure 5: Momentarily pressing the ignition mode switch button once will enter the accessory mode and the amber light will illuminate.</p>

The accessory mode has a 10 minute time out to reduce battery drain. If there is something draining the battery that is causing excessive current draw the vehicle will shut off earlier. That’s why having a good charged battery is so critical on today’s newer vehicles due to the increased electrical demand created by all these vehicle add-ons.

With the ignition off (brake pedal not applied) then pressing and holding the push button start switch for 5 seconds will place the vehicle in run/start mode (ignition on without the engine running). The vehicle will stay powered up for 3 hours and the green LED (run/start) will illuminate (see Figure 6).

Figure 6: When in the RUN/Start mode, the green LED will light up.
<p>Figure 6: When in the RUN/Start mode, the green LED will light up.</p>

After being in run/start mode (ignition on without the engine running) for 1.5 hours, the vehicle will look to see if the transmitter is still present (see Figure 7). If the transmitter is not present in the vehicle, it will power down instead of staying powered up for the full 3 hours.

Figure 7: If the transmitter is not present in the vehicle, the switch will power down.
<p>Figure 7: If the transmitter is not present in the vehicle, the switch will power down.</p>

With the ignition off (brake pedal not applied), then pressing and holding the push button start switch for at least 10 seconds, this will place the vehicle into Vehicle in Service Mode (ignition on without the engine running) and the green LED (run/start) will illuminate. Vehicle in Service Mode is used for service and diagnostics not requiring the operation of the gas engine. The vehicle will stay in Vehicle in Service Mode until the vehicle is manually turned off. Both LEDs have the voltage supplied from the body control module (BCM). The ignition mode switch sends the ignition mode switch status to the passive entry passive start module (peps) and to the BCM. The peps module sends a redundant signal to the BCM with the ignition mode switch status. If for any reason the transmitter is left inside the vehicle while the vehicle is off and the driver’s door has been opened and shut the vehicle will emit a warning sound to alert the driver that the transmitter was left inside the vehicle.

Another warning system is if the vehicle is running and the transmitter is removed from the vehicle, a warning will be displayed on the instrument cluster alerting the driver that the transmitter is not in range.

Diagnosing this system isn’t too hard if you understand it. The ignition mode switch contains two individual switches that provide redundant switch inputs to both the body control module and the keyless entry control module.

The body control module supplies the ignition mode switch a constant battery plus signal. The body control module monitors this signal to determine if the switch is released or pressed. When the ignition mode switch is not pressed, voltage on the signal circuit is pulled down through two resistors in the switch. When the ignition mode switch is pressed, voltage on the signal circuit is pulled down through only one resistor, changing the voltage seen at the body control module and indicating that the ignition mode switch is pressed.

The keyless entry control module monitors voltage on the switch in the same manner as the body control module, but monitors the other individual switch in the ignition mode switch. If for some reason the keyless entry module doesn’t see the correct switch inputs or voltage requirements then a no-start condition will exist.

On this vehicle the power mode master is the BCM. The BCM has multiple battery plus circuits that feed into it. Each of those circuits are partitioned within the controller to drive certain outputs of the vehicle’s body functions. An open or short in any one of the battery plus circuits may induce multiple codes or a section of non-functionality within the BCM with the rest of the BCM functioning normally.

In this case it is useful to refer to the power distribution schematics to determine if the non-functional partition of the controller shares a common battery plus circuit.

The ignition mode switch is a low current switch with a discrete ignition signal to the power mode master for determination of the power mode that will be sent over the serial data circuits to the other modules that need this information.

The power mode master will also activate relays and other direct outputs of the power mode master as needed. The power mode master determines which power mode (Off, Accessory, Run, Crank Request) is required, and reports this information to other modules via serial data.

Modules which have switched voltage inputs may operate in a default mode if the power mode serial data message does not match what the individual module can see from its own connections.

The keyless entry control module also monitors voltage on the switch in the same manner as the BCM, but monitors the second switch located in the ignition mode switch. The keyless entry control module also controls the backup power through the run/crank coil control circuit by applying voltage to the ignition voltage circuit. This circuit is a pass-thru in the BCM and will energize the ignition circuit when the appropriate power mode is required.

Figure 8: The Chevy Traverse PDC is located above the battery and is equipped with high amp fuses.
<p>Figure 8: The Chevy Traverse PDC is located above the battery and is equipped with high amp fuses.</p>

The power mode master receives ignition switch or ignition mode switch signals to identify the operator’s desired power mode. The Chevrolet Traverse has a couple of fuse box or PDC (power distribution centers) that come into play with the push button start system.

The battery PDC (see Figure 8) located on top of the battery is a small fuse center with some good sized high amperage fuses. The front PDC center (see Figure 9) is located on the left front inner fender and houses many more fuses as well. There is another PDC in the rear of the vehicle located behind the left rear inner trim panel.

On any vehicle, knowing where the fuse or electrical PDCs are located is essential in diagnosing any electrical fault. How many times has it happened to you that when asked, “Have you checked all the fuses?” that maybe you thought you did but missed a fuse box that you weren’t aware of?

Figure 9: The front PDC is located on the left front inner fender, with another PDC in the rear, behind the left rear inner trim panel.
<p>Figure 9: The front PDC is located on the left front inner fender, with another PDC in the rear, behind the left rear inner trim panel.</p>

One of the biggest problems I have seen in the automotive industry as far as the repair end of it is concerned is the addition of aftermarket accessories. If an accessory is added to a vehicle and it isn’t installed on the correct circuit then many problems can arise from it. Some of the issues that you will see are power feeds connected to points other than the battery. This can generate a failure.

For example, an accessory was installed on a power feed circuit that is critically monitored by a control module and that module measures an incorrect voltage that it needs and is designed for it then sees it as a problem with that circuit.

The fact is the circuit that’s attached to the OEM circuit is where the fault is at. Can you see that without knowing there was an aftermarket device installed and you didn’t realize it and you started chasing the OEM circuit fault by mistake?

Other aftermarket installation woes could include improper transceiver locations or antennas mounted in the wrong spot. With electromagnetic interference (EMI) and improper shielding, the original manufactured-installed components will be compromised.

The moral of this story is to make sure you check or ask the customer if there are any aftermarket devices installed on the vehicle you are working on. Also check for any service bulletins on the use of aftermarket components as well.

Most of the push button start systems have a conventional metal key that’s usually located on the key fob. That metal key will allow you to access the vehicle for entry in case the vehicle’s door lock system fails or a complete electrical system failure occurs.

There are a few vehicle types that will allow you to remove the push button itself and insert a metal key in the ignition like the 2012 Jeep Cherokee. The start stop button can be removed and the fob with Integrated Key or key fobik can be used in its place, in a similar manner to a conventional key.

This is just one type of system that is destined to visit your shop. There are other components associated with these systems that I didn’t cover in this article. As with any system you work on, make sure you take the time to understand how the system operates. It is extremely important that you have the correct information to tackle these systems and have the correct tools to do the job as efficiently and accurately as you can.

There is a wealth of information out there and it’s pretty much at your fingertips. True, you might not see a vehicle like this 2019 Chevrolet Traverse any time soon, but the push button start technology has been around for a while now.

Working in today’s service bay can create all kinds of challenges. Are you up for the challenge? It's only a push button start away. ■

Edwin Hazzard owns South East Mobile Tech in Charleston, S.C., which is a mobile diagnostic and programming service providing technical service to many automotive and body repair shops. He has 35 years’ experience in the automotive industry. He currently is an automotive trainer, a board member of TST (Technician Service Training), a member of the MDG (Mobile Diagnostic Group), a member of the Professional Tool and Equipment advisory board for Pten magazine, a committee member of Nastaf, and is a beta tester for multiple tool makers.

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