Push-Button Ignition Systems: How to Troubleshoot Start/Stop Problems

Feb. 8, 2021

The typical push button start complaint is “when I push the start button, nothing happens,“ but where do we start to diagnose this complaint when the ignition won’t even turn on?

Today many vehicles only need a smart key fob and a start button or switch to get the vehicle running. These systems aren’t new. They have been around since the late-1990’s. But they have become far more common and we are starting to see issues with them. 

Understanding how a particular vehicle’s push button start system works will be very make- and model- specific, but there are a number of similarities to all push button start systems. 

They will use a smart key fob that contains the needed security information that is specifically matched to the immobilizer system of the vehicle. 

One or more antennae located on the vehicle will be used to sense the fob presence and ask it to report the appropriate security information for interpretation by the immobilizer system. 

Data regarding brake pedal and, if equipped, clutch pedal position is needed, as well as transmission gear position. Some form of steering lock may be used as an added layer of security. And finally, there are a number of modules, wiring and communications networks linking the entire system together to provide the needed voltage to the starter solenoid and other circuits, allowing the vehicle to start and run.

The basics

Push button no-starts should be treated the same way that we have treated no-start situations in the past. The actual vehicle 12-volt battery must be checked thoroughly before we go into any form of high-tech diagnostics. Proper battery voltage, state of charge and the battery’s physical connections are beyond important. You can’t assume that the battery is OK. (I say this from great personal experience.) I certainly don’t trust some diagnostic procedures that claim that honking the horn is an adequate measure of the vehicle’s battery capabilities.

A quick verification of the brake light switch function is next. If the brake lights don’t work, this can be a quick indication of a failed brake switch, blown fuse or wiring issue, and having the brake pedal depressed is needed to make the vehicle start. 
If the basics have been checked and no simple issue is uncovered, it’s time to dig deeper into our diagnostics. But if the ignition won’t turn on, that usually means the scanner isn’t going to function, so what do we do next?

No scanner communications because the vehicle won’t turn on

Installing a scanner is generally the next step, but the ignition won’t turn on, so the scanner is not likely to communicate at first. To get the scanner to function, we will need to manually enter all the vehicle information into it before attempting communications. 

Some vehicles will allow communications with certain theft and body modules by directly going to the appropriate module, but this varies greatly by make and model. Many vehicles won’t allow any scan tool communications until some form of wake-up signal is detected. 

Sometimes this can be done using the key fob and unlocking the doors, or on a Toyota, by turning on and off the courtesy light switch at an interval of 1.5 seconds until communications begins. Volkswagen (VW)/Audi systems can be forced to wake up by turning on the four-way flashers or holding the high beam switch stalk in the flash to pass position. Fords may require the Tear Tag number using the as-built data available at motorcraftservice.com/AsBuilt to initiate communications.

Once the scanner is communicating, it may only provide limited information, data and codes from some modules. Typically, the modules that are all involved in the starting system, steering lock function and the immobilizer will report to help in diagnostics. This limited data will usually give you the info you need about the brake and clutch (if equipped) inputs and transmissions range position, so those areas can be ruled out if a valid key fob is being used and recognized. Pay particular attention to modules that aren’t reporting that need to be reporting, again pointing us in a diagnostic direction.

Immobilizer and smart key fob issues

Most vehicles are quick to tell you on the dash display that there is “no key fob” or “no valid key found” in the vehicle and won’t allow the vehicle to start. The vehicle needs to recognize that a valid key fob is in it before it will allow a start to happen. There will be a number of antennae throughout the vehicle that are looking for and in some cases, talking to the key fob, asking it to respond and share security information.

Dead or weak smart key fob batteries are a common issue, as are improperly installed batteries and damaged fobs from a customer battery replacement or mistreatment. When replacing a smart key fob battery, stay away from cheap, no-name brands. I find they don’t last and may cause other issues, like a low key fob battery light on the dash. 

Unsuccessful key fob recognition by the vehicle is an issue that will cause a no-start condition. Radio frequency interference (RFI) is a common cause of this issue. Removing the battery from the key fob will prevent any of the vehicle’s key fob antenna or antennae assemblies from detecting and trying to verify the key ID code contained in the fob. 

When the key fob is placed near the start button or in the special key fob pocket without the battery, the vehicle will excite the key fob and enable the reading of key ID code and possibly enable the vehicle to start. 

If the vehicle starts using this method, we could be dealing with a key fob recognition error, a problem in the key fob verification system or simply a bad key fob. There are dedicated tools available that will enable you to test smart key fobs, vehicle antennae and their functions. They are available online and aren’t expensive (about $250) and they can be very helpful.

General Motors (GM) has issued a TSB or diagnostic tip GM # PIC5650H for a no-crank, no-start, no-key fob-detected concern. GM says that RFI can “jam” the frequency being transmitted from the key fob. This interference can be coming from a number of sources located inside the vehicle, Parking cards, building access cards or even other vehicle key fobs can be the cause. But GM also claims that some aftermarket LED lights, USB power bars and even certain cell phone chargers can cause RFI, resulting in a no-start condition.

Some Mazdas may not start after a vehicle battery failure or replacement. If code B13D3 “unregistered remote transmitter” is detected, a vehicle immobilizer system registration may need to be performed. Mazda uses a similar immobilizer system to Ford PATS and two functioning key fobs will be required to perform the registration.

Steering lock concerns

The steering column lock is an added layer of security on some push button start vehicles, but on those vehicles it is also an integral part of the push button start system. 

When the start button is pushed, the steering lock motor or steering lock control module assembly will be asked to release the steering column and report its functionality and health to other modules. If that information isn’t transferred to the appropriate modules because of a malfunctioning steering lock motor, steering lock micro switch or steering lock module or the wiring in the column is damaged, a no-start situation can result.

Be sure to ask the customer experiencing the no-start condition if they have seen any strange dash messages in the days or weeks before the failure. VW/Audis may display a “Steering Defective! Do not drive vehicle!” message, with a no-start condition, but the customer may not even notice and then retry starting. The steering lock motor may release and act normal and function properly for days or even weeks again before acting up. This situation may or may not set trouble codes.

The VW/Audi Electronic Steering Column Lock is a common failure and typically won’t respond when being scanned, but there will be immobilizer codes.

One of the cheapest, easiest tools that I use to detect a steering lock issue are my own ears. Sitting in the vehicle with the doors closed, I will do the normal starting sequence while listening to the steering column. I have even used a stethoscope to listen for the motor to release. If no noise is heard, I will try to gently rattle the steering wheel while pushing the start button with my foot on the brake pedal. This rattling may activate the steering lock motor from a possible dead spot or close a failing micro switch. Mercedes-Benz, Nissan, VW/Audi and some Kia/Hyundais experience this issue. If the vehicle starts after rattling the steering wheel or gently tapping on the steering lock module in a Kia, you are likely in the correct area. 

If you suspect that the steering lock control or motor assembly is the issue, they can be inspected for power, ground and the communication network using an oscilloscope or good digital volt ohm meter, or DVOM. Very rarely will you be able to jump anything or even open the module to clean any micro switches. Replacement will be the answer.

Most pieces of the security system, including the steering lock module/motor, may need to be flashed or programmed once diagnosed and installed. This procedure may require the need for security clearance and a valid locksmith license. Be sure to check not only your scanner’s capabilities, but also whether or not you can obtain the needed security authorizations before committing to these types of repairs. Note that used parts typically can’t be used for replacement as security parts can only be programmed, matched or flashed once. 

Understanding the particular push button starting system that you are working on is imperative. There are similarities in how these systems function, but there can be huge differences even between models on the same vehicle platform. 

A good, up-to-date information system will usually provide the needed diagnostic trouble tree on how to perform a push button no-start investigation. Looking at the wiring diagrams will show what modules are involved and their respective power, ground and communications lines that can be checked.

We all know that technology doesn’t stop and only moves forward. The push button start system is not going to stand still. Cell phone technology has allowed BMW, Mercedes-Benz and Hyundai to create digital car keys, stored on your cell phone.

Technology is changing and the use of a smart key fob is likely to fade away, just like the traditional ignition key and cylinder is fading now.  

About the Author

Jeff Taylor

Jeff Taylor boasts a 30-plus year career in the automotive industry as a fully licensed professional lead technician. Jeff works for the CARS Training Network Inc. in Oshawa, Ontario, Canada. He is also heavily involved in government focus groups, serves as an accomplished technical writer and he has completed in international diagnostic competitions as well as providing his expertise as an automotive technical instructor for a major aftermarket parts retailer.