P2687: Fuel Supply Heater Control Circuit/Open
What to do
In warm weather you will notice absolutely nothing, and that is the trap. Fix this anyway.
This heater keeps diesel warm enough that the wax naturally present in it does not crystallise and block the fuel filter. Above about freezing it has nothing to do, so a dead one is completely invisible — the car starts and runs perfectly and the only sign is this code.
The bill comes in winter. On a hard frost, a vehicle with no working fuel heater can block its filter with wax and simply not start, or start and cut out within a minute. It is a common way to be stranded, and cranking does not help — the only thing that clears wax is warmth, so it usually means recovery to somewhere heated and a filter change.
So the practical advice is: do not defer this because nothing seems wrong. A code that appears in summer is a warning you have been given six months early. Getting it done before the first cold snap is a routine job; getting it done afterwards is a recovery truck.
Ask for the relay and the heavy connections to be checked as well as the element — this circuit draws a lot of current, and burnt contacts are commoner than a failed heater.
What this code means
An open circuit in the control of the heater that warms diesel fuel before it reaches the filter.
This is the most seasonal code in the corpus, and that is exactly what makes it dangerous to ignore.
Diesel is not a single substance but a blend, and part of that blend is paraffin wax. As fuel cools, that wax comes out of solution as crystals — first clouding the fuel, then growing large enough to block the pores of a filter designed to stop particles many times smaller. The temperature at which this starts is a property of the fuel, and while winter-grade diesel is blended to push it lower, the margin is not large in a hard frost. A blocked filter stops fuel reaching the engine entirely: the vehicle cranks and will not start, or starts and dies within a minute.
A fuel supply heater exists to keep the fuel above that point — an electric element in the filter housing, in the fuel line, or sometimes fuel returned warm from the engine.
Here is the part that costs people a morning, and it is the whole reason this page argues the way it does. A dead fuel heater has no symptom whatsoever in warm weather. The engine starts perfectly, runs perfectly, uses the same fuel and makes the same power. The only evidence is this code — and a code with no symptom attached is precisely the kind that gets cleared, deferred, or dismissed as a sensor fault.
So the fault is discovered in July and paid for in January. The vehicle that would not start on the coldest morning of the year, with a filter full of wax, is very often one that stored this code six months earlier.
The advice that follows is unusually simple: fix it when it appears, regardless of the season, and treat a summer occurrence as a winter problem you have been warned about early. Fitting a heater element in mild weather is an ordinary job. Doing it at the roadside in a frost, with a waxed filter, is not — and no amount of cranking clears wax, because the only thing that removes it is warmth.
The circuit itself carries substantial current, so as with the intake air heater at P2605, relay contacts and heavy connections outrank the element as causes.
Likely causes
Start here
- Corroded or loose connector · easy
- Open circuit in heater wiring · moderate
- Faulty fuel supply heater · moderate
Less common
- Blown fuse supplying the heater circuit · easy
- High resistance in heater wiring · moderate
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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