Skip the auto shop - Our mechanics make house calls
  1. Home
  2. Articles
  3. How Long Does a Main Relay (Computer/Fuel System) Last?

How Long Does a Main Relay (Computer/Fuel System) Last?

main relay

The main computer relay is responsible for supplying power to the Powertrain Control Module (PCM). The PCM is the primary computer that controls the operation of the engine, transmission, emission control system, starting system, and charging system. Other systems not directly related to emissions have some amount of PCM control.

Several symptoms are possible whenever a PCM relay starts to fail.

1. Intermittent no-crank or no-start condition

It is possible for a relay to fail intermittently. This creates a condition where the engine may crank but not start. It can also prevent the engine from cranking at all. The PCM has no power to energize the fuel injection system and the ignition system, which leads to the no-start condition. At other times, the engine will start and run normally. The most common cause of an intermittent relay failure is an open circuit inside the relay itself, usually from open soldered joints.

2. Engine not cranking or starting at all

When the PCM relay has failed completely, the engine will either not crank or not start at all. The PCM isn’t the only possible cause of a no-crank/no-start, however. Only a trained technician like those at YourMechanic would be able to determine what the actual cause is.

3. No scan tool communication with PCM.

A failed PCM relay will not allow the PCM to power up. When this happens, the PCM will not be able to communicate with any diagnostic scan tool. For a technician, not being able to communicate with the PCM increases the complexity of diagnosis.

If the relay has failed, it needs to be replaced.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
Icon-warranty_badge-02

Skip the repair shop, our top-rated mechanics come to you.

At your home or office

Choose from 600+ repair, maintenance & diagnostic services. Our top-rated mechanics bring all parts & tools to your location.

Fair & transparent pricing

See labor & parts costs upfront, so you can book with confidence.

12-month, 12,000-mile warranty

Our services are backed by a 12-month, 12,000-mile warranty for your peace of mind.

Get A Quote

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.

GET A QUOTE

More related articles

Veteran and Military Driver Laws and Benefits in Idaho
The state of Idaho offers a number of benefits and perks for those Americans who have either served in an Armed Forces branch in the...
P2159 OBD-II Trouble Code: Vehicle Speed Sensor B Range/Performance
Diagnostic Trouble Code (DTC): P2159 P2159 code definition Vehicle Speed Sensor B Range/Performance...
P2422 OBD-II Trouble Code: Evaporative Emissions Control System (EVAP) Vent Valve Stuck Closed
Diagnostic Trouble Code (DTC): P2422 P2422 code definition Evaporative Emissions Control System (EVAP)...

Related questions

Q: Starting issue - 2009 Vauxhall Corsa

Hello there, many common faults will cause your 2009 Corsa to not start. You have done well in replacing the starter motor as this is a common failure point. The first place to start is to have the battery load...

Q: When I put gas in, after a few seconds it spits it back out.

Hi there. The fuel vent hose on the fuel filler neck is plugged and not allowing the fuel to vent as the tank is filled up. You may have to remove the rubber hose to the tank and take a...

Q: Why does my car only run if we bypass the fuel pump relay on my 1998 Acura RL

Hi there. If the car will run with the relay bypassed then the fuel pump is fine. If the relay is fine also then the control for the circuit has a failure. Most of the time this is caused by...