What do engine mounts have to do with a wiring code?

More than you would expect on this particular run of harness. The loom serving the far bank's exhaust side passes through the narrow gap between the engine and the firewall or subframe, and that gap is not a fixed size — the engine hangs on rubber mounts that allow a controlled amount of movement. When a mount's rubber collapses or separates, the engine sits lower and rocks much further under load, and anything in that gap gets squeezed. That produces a short that shows up under hard acceleration and disappears at idle. Repairing the wire without replacing the mount means doing the same wiring job again in a few months.

How do I tell whether rodents caused this?

Look for evidence rather than for the bite marks alone, because the damaged section may be somewhere you cannot see. The area behind the engine is warm, dark and sheltered, which makes it a favourite nesting spot, so check on top of the transmission, in the cowl area and around the bulkhead for shredded insulation, foam, nesting material, seed husks and droppings. There is usually a smell as well. The important part is what you do after finding it: rodents rarely damage a single wire, so if the evidence is there, inspect the whole loom before repairing the one conductor that happened to set a code.

I cannot see any damage when I look down at the harness. Am I missing something?

Almost certainly the angle. A short to ground happens where the loom is touching something, which means the damage is on the face pressed against that surface — the side you cannot see from above. Raise the vehicle, work from underneath, and physically lift and roll each section of loom so the hidden face comes into view. Run your fingers along it too; a flattened or crushed section can be felt before it can be seen, and it will point you at whatever it has been pressing against.

Can I drive it until I can get it in?

Mechanically yes. The exhaust phaser rests at its default position, the engine runs normally and there is no damage accumulating in the valvetrain. Two things temper that. A circuit shorted to ground is pushing current through a driver inside the module that was not designed to carry it indefinitely, and modules cost far more than solenoids. And if the underlying cause is a failed engine mount, the excess engine movement is working on more than just this one loom, so it is worth having looked at sooner rather than later.

OBD-II trouble code

P0085: Exhaust Valve Control Solenoid Circuit Low (Bank 2)

The bank 2 exhaust valve control solenoid circuit is shorted to ground. On this run of harness the cause is more often something mechanical pressing on the loom than the gradual abrasion people expect — worn engine mounts and rodent damage both belong on the suspect list.

Medium severityPowertrainVariable Valve TimingDrivable short-term

Quick facts

System: Powertrain
Category: Variable Valve Timing
Severity: Medium severity
Drivable: Usually safe to drive short-term
Repair cost range: $130 – $1,200
DIY difficulty: Advanced DIY

What does P0085 mean?

P0085 sets when the module sees the control circuit for the bank 2 exhaust valve control solenoid held below its expected voltage. Somewhere the circuit has found a path to ground that it should not have.

The harness branch involved here occupies the least visible real estate under the bonnet. On a transverse V engine it runs across and behind the engine towards the far cylinder head's exhaust side — a space nobody looks into during routine service, that no light reaches, and that on many cars is only properly visible from underneath. That location shapes the failure population in a way that is worth planning your inspection around, because two of the likeliest causes are not electrical faults at all.

The first is crushing rather than chafing. Behind the engine, the gap between the engine and the firewall or the subframe is small and it is not a fixed distance. The engine hangs on rubber mounts that are designed to let it move a controlled amount and that lose that control as they age. A mount with a collapsed or separated rubber isolator lets the engine sit lower and rock further under load than it was ever meant to, and the loom in that gap gets squeezed against structure every time the driver accelerates hard or reverses up a driveway. The result is a short that appears under specific driving conditions and vanishes at idle on a ramp. If you find crushed or flattened loom back there, replacing the wire without replacing the mount guarantees a repeat, and the mount is the actual repair.

The second is rodent damage. The area behind the engine is warm, sheltered, dark and close to the bulkhead, which makes it one of the two or three places on a vehicle where nesting reliably happens. Chewed insulation produces exactly this code, and there are tell-tales worth looking for before you get the meter out: shredded insulation or foam, seed husks, droppings, nesting material on top of the transmission or in the cowl, and a distinctive smell. Rodent damage is also rarely limited to one wire, so if you find it here, inspect the whole loom rather than repairing the one conductor that logged a code and calling it done.

The conventional causes are still present, of course — a winding shorted turn to turn, moisture bridging terminals inside a connector, insulation hardened by exhaust heat until it splits. But an inspection that only considers the wire itself will miss the two causes above, and both of them have a second repair attached that the wire repair alone will not address.

One more practical note. Because this location is difficult to see from above, the productive way to inspect it is from underneath with the car raised and with the loom lifted and rolled so the hidden face is visible. A short to ground almost always shows on the side of the loom that is resting against something, which is by definition the side you cannot see when you look down at it.

The engine keeps running normally with the exhaust phaser parked, so this is not an urgent repair mechanically. It is worth attending to because a circuit shorted to ground is passing current through a module driver that has to absorb it.

Common causes

Loom crushed between the engine and the firewall or subframe because a failed engine mount lets the engine move too far
Rodent damage to insulation in the sheltered space behind the engine
Control wire shorted to ground where heat-hardened insulation has split on the exhaust side of the far head
Exhaust valve control solenoid with a winding shorted turn to turn
Water or coolant intrusion into the connector creating a conductive bridge
Loom trapped under a bracket, heat shield or bellhousing bolt during previous work
Missing or displaced heat shield leaving the harness exposed where it was never meant to be
Failed low-side driver in the module holding its own output down
Aftermarket wiring routed through the same gap and abrading the engine loom

Symptoms

Check engine light on with P0085 stored
Fault that appears under hard acceleration or heavy engine load and clears at idle
Little change in how the vehicle drives
Slight fuel economy loss and elevated oxides of nitrogen
Engine movement, clunking or vibration suggesting a failed mount
Nesting material, droppings or shredded insulation found on top of the transmission or in the cowl
Other unrelated circuit faults in the same loom, typical of rodent damage
Solenoid output shut down by the module after an overcurrent event

Diagnostic steps

1.Raise the vehicle and inspect the harness branch behind the engine from underneath, because this run cannot be properly seen from above.
2.Lift and roll the loom so the hidden underside is visible, since a short to ground shows on the face that is resting against something.
3.Check the engine mounts for collapsed, separated or oil-soaked rubber, and watch how far the engine moves when the throttle is snapped with the vehicle in gear and the brake held.
4.Look for crushed or flattened sections of loom in the gap between the engine and the firewall or subframe.
5.Search for signs of rodent activity — shredded insulation, nesting material, droppings, seed husks on top of the transmission or in the cowl.
6.If rodent damage is found, inspect the entire loom rather than repairing only the conductor that set the code.
7.Disconnect the solenoid and measure resistance from the harness-side control terminal to ground with the ignition off.
8.Measure the solenoid coil resistance across its own terminals and compare it against the bank 1 exhaust solenoid.
9.Confirm all heat shielding in the area is present and correctly located before closing up.
10.Replace any failed engine mount as part of the repair, not as a separate job, or the harness damage will simply happen again.

Repair cost

$130 – $1,200

Diagnosis is $90 to $180 and usually needs the car raised. An exhaust valve control solenoid is $35 to $240 in parts with 0.8 to 3.5 hours of labour at this position, giving $250 to $950 fitted. Harness repair behind the engine is $200 to $500 because of the access and the high-temperature materials the location demands. The two causes that carry a second line item are the ones people forget to budget for: an engine mount is $80 to $350 fitted and leaving it turns the wiring repair into a repeat visit, while rodent damage extends well beyond one wire and section repairs of a chewed loom commonly run $300 to $1,200 depending on how many circuits were reached.

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DIY vs shop

This is an advanced DIY job. It typically requires specialty tools, scan-tool access, lifting equipment, or careful sequencing to avoid causing new failures. Plan for extended downtime and have a backup vehicle. Most owners are better served by a shop that has done this repair before.