P0685 OBD-II Trouble Code: ECM/PCM Power Relay Circuit Malfunction

Our certified mechanics come to you · Get a fair and transparent estimate upfront

Red-stars EXCELLENT RATING ON

Cost of diagnosing the P0685 code

P0685 is a diagnostic trouble code (DTC) for "ECM/PCM Power Relay Circuit Malfunction". This can happen for multiple reasons and a mechanic needs to diagnose the specific cause for this code to be triggered in your situation. Our certified mobile mechanics can come to your home or office to perform the Check Engine Light diagnostic. Once we are able to diagnose the problem, you will be provided with an upfront quote for the recommended fix and receive $20.00 off as a credit towards the repair. All our repairs are backed by our 12-month / 12,000-mile warranty.

Cars Estimate Credit towards follow-up repair Earliest Availability
Ford$20.00
Toyota$20.00
BMW$20.00
SCHEDULE P0685 DIAGNOSTIC Get a fair and transparent estimate upfront

P0685 code definition

P0685 is the fault code for ECM/PCM Power Relay Control Circuit /Open.

What the P0685 code means

The PCM (powertrain control module) receives data about the vehicle’s operating conditions from various areas in the system. In order to work properly, the PCM is supplied with power by a relay, which uses a battery voltage signal, a ground signal, and an ignition switch input signal. The voltage in the relay coil control circuit is normally low. If you see trouble code P0685, it means that the PCM’s fault detection circuit has detected voltage from the relay that measures above the normal parameters – above 4.6 volts with the key turned on.

What causes the P0685 code?

As with any trouble code, there could be a wide variety of potential causes. One of the most common is simply a bad PCM relay. Other possibilities include a blown fuse, a shorted circuit, a faulty connection, battery problems such as a cable defect, and rarely, a bad PCM or ECM.

What are the symptoms of the P0685 code?

The Check Engine light may come on, although the vehicle may still run. Depending upon the source of the problem, the vehicle may crank but not start, or it will start but suffer from reduced power – or “limp” mode.

How does a mechanic diagnose the P0685 code?

The first step in diagnosing any trouble code is typically to record the stored codes and freeze frame data using an OBD-II scanner. Any other codes that come up should be investigated and fixed in the order in which they happened. The vehicle will then be retested to make sure the P0685 code returns (if not, it may be an intermittent condition, which can make diagnostics more complicated).

Next, the technician will remove the powertrain relay and test the control circuit to determine if it is functioning properly. Other terminals and connectors may also be tested to locate the interruption in the power source. The mechanic will also perform a visual inspection of the battery cables, as corrosion or loose connections can affect the PCM/ECM relay. Once all of these tests and any necessary repairs have been completed, the vehicle will be tested to see if it runs and if the code returns. If the problem hasn’t been solved, the PCM itself could be faulty.

Common mistakes when diagnosing the P0685 code

Because this code is related to a complex network of electrical components, it’s easy to rush to judgement and simply replace the PCM, when in fact this isn’t usually the problem and is a very costly repair. Corroded battery cables or a loose connection often cause issues with the PCM relay, so these should be a routine part of the inspection.

How serious is the P0685 code?

Even if your vehicle runs while setting this code, it could at any moment decide to stall out, or refuse to start. Vital safety components may also be affected – for example, your headlights could suddenly go out, which would be dangerous if you’re driving at night when this happens. If you’re experiencing symptoms of a problem such as the radio not working, you should have the problem diagnosed and repaired by a professional as soon as possible, to avoid further damage to other components.

What repairs can fix the P0685 code?

Necessary repairs for a faulty PCM/ECM power relay control circuit may include:

Additional comments for consideration regarding the P0685 code

This is one of those codes that could be a very simple fix, such as a bad battery or battery cables, or more complex, and require multiple tweaks and repairs. Always consult a professional for help in unfamiliar territory, in order to avoid causing further damage or replacing expensive parts that may not be faulty.

Need help with a P0685 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

trouble codes
Check Engine Light
P0685

No more waiting rooms! Our mechanics will come to you to diagnose and fix the P0685 code.

SCHEDULE P0685 DIAGNOSTIC
Get a $20 credit for the follow-up repair

Recent Check Engine Light is on Inspection reviews

Excellent Rating


YourMechanic Check Engine Light is on Inspection Service

Average Rating

4.8/5

Number of Reviews

5,156

Rating Summary
4,752
196
50
27
131
4,752
196
50
27
131

Al

21 years of experience
14 reviews
Al
21 years of experience
Nissan Pathfinder - Check Engine Light is on - Atlanta, Georgia
Al, was cool and very knowledgeable. Being direct and upfront always works. Al, is a credit to the company.

Xavier

10 years of experience
20 reviews
Xavier
10 years of experience
Chevrolet Equinox - Check Engine Light is on - Frisco, Texas
Xavier was GREAT!!! He made sure that I understood everything that he did to my vehicle and answered all my questions. Very thorough and even worked thru the light rain that we had. When I have to use this service again, I hope to be able to request him!

Luis

14 years of experience
52 reviews
Luis
14 years of experience
Kia Sorento - Check Engine Light is on - Las Vegas, Nevada
Luis did an excellent job in determining that this was a warranty issue on bad parts. He has integrity and is good at what he does. I would highly recommend him for any auto repairs that come up.

Reginald

36 years of experience
32 reviews
Reginald
36 years of experience
BMW 325i - Check Engine Light is on - Los Angeles, California
Reginald was incredibly helpful in helping me to diagnose several issues in my car, as well as repair issues to help me pass a break and light test. He even went so far as to come to the brake and light testing location so that he could ensure that the car passed and be there if anything else needed to be fixed on the spot. Absolutely would recommend him to anyone who is looking for an honest and knowledgeable mechanic!


Related questions

Car starts, then stalls in one second.

Hi there. This can be a computer issue, but from the codes and the issue it sounds more like a voltage problem. If there is low voltage from a bad battery or a bad connection then the vehicle will act...

I have a 2006 Honda Accord and the dash lights and radio willl sometimes go off then come right back on when I'm going about 40 mph.

The code P0685 refers to the main ECM (computer) relay has lost power. Check the main relay and see if its getting hot. A hot relay will disconnect to cool off and reconnect. If the relay is getting hot, then...

More related articles

P0403 OBD-II Trouble Code: Exhaust Gas Recirculation Circuit Malfunction
P0403 code definition Exhaust Gas Recirculation Circuit Malfunction What the P0403 code means P0403 is an OBD-II generic code that indicates that...
OBD-II Trouble Code P0688: ECM/PCM Power Relay Sense Circuit/Open
P0688 means there is an output circuit issue in the power relay sense circuit, likely due to a damaged or defective ECM relay or faulty wiring.
P2227 OBD-II Trouble Code: Barometric Pressure Circuit Range/Performance
P2227 trouble code definition Either the barometric pressure sensor is providing a reading that does not correspond to the parameters of the...

How can we help?

Our service team is available 7 days a week, Monday - Friday from 6 AM to 5 PM PST, Saturday - Sunday 7 AM - 4 PM PST.

1 (855) 347-2779 · hi@yourmechanic.com