If your generator does not start automatically during a power outage, first check whether the generator controller is in Auto mode and whether the ATS is actually sending a remote start signal.

In our experience, if the generator starts normally in Manual mode but does nothing after utility power fails, I normally check the ATS start contact, controller remote-start input and control wiring before looking for an engine problem.

If the controller receives the start command and the engine cranks but does not start, the problem has already moved beyond the ATS automatic start sequence. At that point, I would troubleshoot the generator starting or engine system instead.

What Should You Check First?

When we troubleshoot an automatic start problem, I first find out where the sequence stops:

Utility fails → ATS detects utility failure → ATS sends start signal → Generator controller receives signal → Generator starts

This is more useful than starting with the question, “Which part is bad?”

What Happens	What I Would Check First
Generator starts in Manual but does nothing in Auto	Auto mode, ATS start contact, remote start input and control wiring
ATS detects utility failure but no start signal reaches the generator	ATS start output/contact, start delay and wiring
Controller receives the remote start signal but there is no crank	Controller status, alarms, start permissive and starting circuit
Generator cranks but does not start	Generator starting, fuel or engine system
Generator starts but ATS does not transfer	Generator voltage/frequency, ATS sensing and transfer conditions

For me, Manual mode is one of the quickest dividing lines in this fault.

If the generator starts cleanly in Manual, I usually leave the engine side alone at first and follow the automatic start circuit. If it also fails in Manual, I stop treating the problem mainly as an ATS fault.

1. Is the Generator Controller in Auto Mode?

This sounds simple, but I always check it first.

A healthy generator will not respond to an ATS remote start command if its controller has been left in Manual, Stop or another mode that does not permit automatic starting.

We often see this after maintenance or generator testing. The technician starts the generator manually, finishes the work, but the controller is not returned to Auto.

Before going deeper, check:

• Is the controller in Auto mode?
• Is there an active shutdown or alarm?
• Is the emergency stop active?
• Does the controller allow a remote start?

The exact indication depends on the controller. Deep Sea, ComAp, SmartGen and other controllers use different inputs, settings and logic.

I would not start changing parameters yet. First confirm the operating mode and current controller status.

2. Does the ATS Actually Detect the Utility Failure?

If the generator is ready in Auto, I look at the ATS next.

The ATS must recognize that the utility source is no longer acceptable before it can start the standby generator.

Depending on the system, the ATS may monitor conditions such as:

• Utility voltage
• Frequency
• Phase condition
• Phase sequence
• Under-voltage or over-voltage
• Mains failure delay

One detail is easy to overlook: the generator may not be designed to start the instant utility power disappears.

Some systems use a mains-failure or start delay to avoid starting the generator during a very short utility disturbance. The actual delay depends on the ATS settings and project design.

So before assuming there is a fault, allow for the programmed delay and check the ATS status.

Does it indicate Utility Normal, Utility Failure, Mains Failure, or an equivalent condition?

I also make a distinction between:

“The load has lost power”

and

“The ATS has detected a utility failure.”

These are not necessarily the same.

For example, an upstream or downstream breaker problem can interrupt power to the load while the ATS sensing circuit still sees normal utility voltage. A sensing fuse, control power or wiring problem can also prevent the ATS from correctly detecting the source condition.

3. Is the ATS Sending the Generator Start Signal?

If the ATS correctly recognizes the utility failure and the programmed delay has expired, the next question is simple:

Did the start command leave the ATS?

In many standby systems, the ATS uses a dry contact to send a remote start command to the generator controller.

If the generator works normally in Manual but does nothing in Auto, this is one of the first control points I want to confirm.

Possible causes include:

• ATS start contact not operating
• Start relay or output fault
• Incorrect ATS control logic
• Loose or broken control wiring
• Incorrect terminal connection
• Control fuse or control power problem
• A timer or permissive condition preventing the command

This is why I do not replace an ATS simply because the generator did not start.

The ATS may have detected the utility failure correctly but failed to issue the command. Or it may have issued the command and the problem is somewhere between the ATS and generator controller.

Those are very different faults.

4. Does the Generator Controller Receive the Remote Start Signal?

The next dividing point is the generator controller.

If the ATS start output changes state but the controller does not recognize a remote start request, I focus on the circuit between them.

Typical areas include:

• Loose terminals
• Broken control wires
• Incorrect connections
• Wrong controller input configuration
• Poor relay or terminal contact
• Wiring changes made during previous maintenance

This is especially important when the generator starts normally from its own controller.

If I can start the generator manually and it reaches normal running condition, I already know a lot about the machine. I would not immediately start replacing the battery, starter motor or engine components.

I would first find out why the automatic start command is not reaching or being accepted by the controller.

5. What If the Controller Receives the Signal but the Generator Does Not Crank?

Now the fault has moved downstream again.

If the controller clearly shows a remote start request but does not initiate cranking, I would check the controller status and the conditions required to allow a start.

Possible areas include:

• Active shutdown alarms
• Emergency stop circuit
• Battery or DC control supply
• Starting circuit
• Starter relay
• Controller start output
• Start permissive or interlock
• Controller configuration

At this point, I compare Auto operation with Manual operation.

If Manual Start works, I continue looking at the automatic control logic and the way the remote start request is being processed.

If Manual Start also fails, the ATS becomes much less interesting to me. I would move to the generator starting system.

That simple comparison can prevent a lot of unnecessary ATS troubleshooting.

6. What If the Generator Cranks but Does Not Start?

Once the controller accepts the start request and the engine begins cranking, the ATS has normally completed its main role in the automatic start sequence.

Now I would investigate the generator itself.

Possible areas include:

• Battery condition and cranking speed
• Fuel supply
• Fuel shutoff system
• Engine protection circuit
• Engine or controller alarms

There is no benefit in turning this ATS article into a complete engine troubleshooting guide.

The important diagnosis is:

ATS sends start command → Controller receives command → Engine cranks

If all three happen, the automatic start control chain is probably working. The next job is to find out why the engine cannot complete the start.

7. What If the Generator Starts but the ATS Does Not Transfer?

This is a different fault path.

A running generator does not automatically mean the ATS is ready to transfer the load.

The ATS normally needs to confirm that the generator source is acceptable. Depending on the design, this may include:

• Generator voltage
• Frequency
• Phase condition
• Phase sequence
• Generator available status
• Warm-up or transfer delay

If the engine starts normally but the ATS remains on utility, I stop troubleshooting the remote start circuit.

I first check whether the ATS actually recognizes the generator source as available and acceptable.

For example, the engine may be running normally while generator voltage is missing or outside the acceptable range. In that situation, the ATS may be doing exactly what it should by refusing to transfer.

Only after the generator source and transfer permissive conditions are confirmed would I start suspecting the transfer mechanism itself.

A Quick Way to Locate the Fault

When we troubleshoot this type of system, these are the questions I want answered:

Did the ATS detect the utility failure?
If no, check utility sensing, control power and related ATS settings.

Did the ATS send the generator start command?
If no, check the start delay, ATS output/contact and control logic.

Did the generator controller receive the command?
If no, check the control wiring and controller input.

Did the generator crank?
If no, check controller status, alarms, interlocks and the starting circuit.

Did the engine start?
If no, move into generator starting and engine troubleshooting.

Did the generator start but the load still has no power?
Check generator voltage/frequency and the ATS transfer sequence.

This is the troubleshooting order I prefer because each answer removes part of the system from suspicion.

Can You Check an Automatic Start Problem Safely?

There are several things you can check without opening the ATS cabinet:

• Generator controller operating mode
• Controller alarms
• ATS status indication
• Whether the generator starts in Manual mode
• What happens during a properly authorized automatic test

Internal electrical testing is different.

An ATS cabinet may contain both utility and generator power sources. Stopping the generator does not mean the utility side is dead. Losing utility power also does not mean the generator side cannot suddenly become energized if Auto Start is enabled.

Internal ATS measurements, live voltage testing, control circuit testing and work around breakers, contactors or motorized transfer mechanisms should be performed by technicians who understand the system and its isolation procedure.

I would also never bypass an electrical or mechanical interlock simply to force a transfer.

Why I Do Not Blame the ATS First

The visible symptom is simple:

Utility fails and the generator does not start.

But several different faults can create exactly that symptom.

The generator may have been left in Manual mode. The ATS may not detect the utility failure. The ATS may detect it but fail to send the start command. The signal may be lost in the control wiring. The controller may receive the signal but refuse to start because of an alarm or interlock.

That is why I prefer to locate the failed step before deciding that any component needs replacement.

In our experience, replacing parts before confirming the start sequence usually makes troubleshooting slower, not faster.

How Can You Prevent This Problem?

A standby generator should not be tested only by pressing its Manual Start button.

That proves the generator can start. It does not prove that the complete automatic standby system works.

During periodic testing, I prefer to confirm the whole sequence:

Utility failure detected → Start command → Generator starts → Voltage/frequency stabilize → ATS transfers → Load receives generator power → Utility returns → ATS retransfers → Generator cools down and stops

This checks the generator, ATS and control system together.

It is also worth checking controller alarms, battery condition, control wiring and terminal condition during scheduled maintenance.

Need Help Finding Where the Start Sequence Stops?

If your generator starts normally in Manual mode but will not start automatically during a power outage, the ATS or generator controller does not necessarily need to be replaced.

You can send us the ATS model, generator controller model, wiring diagram, controller alarm/status information, and tell us what happens after utility power fails.

We normally start by identifying whether the sequence stops at the ATS utility sensing, ATS start output, remote start wiring, controller input or generator starting stage. Once that point is clear, it is much easier to decide what actually needs to be tested or repaired.