I have this code and the same fault on the other bank. Do I need two solenoids?

Almost certainly not, and this is the most useful thing to know about P0079. Two solenoids mounted on opposite cylinder heads, in separate harness branches, do not develop internal shorts on the same day. What they do share is a supply feed, a ground path, a splice where the branches separate, and the module itself. When both banks report the same fault the cause is in the shared element by elimination. Find the point where the two branches diverge and test upstream of it. Buying two solenoids here typically means several hundred dollars spent and both codes still stored.

I also have a camshaft timing code on this bank. Which do I fix first?

The electrical one, and the order is not arbitrary. A solenoid whose circuit is shorted cannot be controlled, so the phaser cannot reach the position the module commanded, and the timing correlation code is the module noticing that consequence. Repair the circuit, clear both codes and drive it. If the timing code returns with the electrical circuit proven healthy, then the phaser or the chain deserves attention. Doing it the other way round leads to expensive mechanical work on hardware that was only ever obeying a broken command.

My engine is a four-cylinder, so there is no second bank. How do I use that test?

You use its logic with a different instrument. On an inline engine there is no bank 2 solenoid and no partner code will ever appear, so the shared-versus-local question has to be settled by measurement. Disconnect the solenoid and check whether the low condition still exists at the module's control terminal. If it clears once the solenoid is out of the circuit, the winding was the short. If it persists with nothing connected, the fault is in the wiring or the module. Same reasoning, one connector instead of a code pattern.

Is it safe to keep driving?

Mechanically, yes. The exhaust phaser parks at its default position, power delivery is largely unchanged, and most drivers notice nothing beyond the warning light. The real costs are a small fuel economy penalty and a rise in oxides of nitrogen that can fail an emissions test. The reason not to leave it indefinitely is electrical rather than mechanical: a circuit shorted to ground is pulling current through a module driver that was not designed to sustain it, and modules are considerably more expensive than solenoids.

OBD-II trouble code

P0079: Exhaust Valve Control Solenoid Circuit Low (Bank 1)

Voltage on the bank 1 exhaust valve control solenoid circuit is being held low. Whether this code arrives alone or alongside its bank 2 twin is the most informative thing about it — two solenoids on opposite cylinder heads do not fail on the same day.

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: $100 – $650
DIY difficulty: Intermediate DIY

What does P0079 mean?

P0079 means the module measured a voltage below the expected level on the control circuit for the bank 1 exhaust valve control solenoid. Something is providing a path to ground that should not be there, or the module's own output is being held down.

The most efficient way into this code is not a meter but a full code read, because the pattern of which codes are present tells you where to look before you touch anything. Consider three situations.

P0079 stored on its own, with no other faults, points at something local to the bank 1 exhaust solenoid: its winding, its connector, or the short run of harness that serves it. That is the ordinary case and it is a contained diagnosis.

P0079 stored together with P0085, the equivalent low circuit fault for the bank 2 exhaust solenoid, is a completely different proposition and it should stop you from touching either solenoid. Two solenoids mounted on opposite cylinder heads, in separate harness branches, do not develop internal shorts on the same day. What they do share is a supply feed, a ground path, a common connector or splice where the branches separate, and a module. When both banks fail identically the fault is in the shared element by simple elimination, and the correct move is to find the point where the two branches diverge and test upstream of it. Replacing solenoids in this situation is a way to spend money twice and still have both codes.

P0079 accompanied by an exhaust camshaft timing correlation code on the same bank is the third pattern, and the order of causation matters. The electrical fault came first and the timing complaint is its consequence, because a solenoid that cannot be controlled cannot put the phaser where the module asked. Repair the circuit, clear both codes, and only investigate the phaser if the timing code returns with the electrical circuit proven healthy. Chasing the timing code first leads to a phaser or a chain job that was never needed.

One important qualification on the two-bank test: it only exists if the engine has two banks. On an inline four or six there is no bank 2 exhaust solenoid and no partner code will ever appear, so the shared-versus-local question has to be answered by measurement instead. Disconnect the solenoid and see whether the low condition persists at the module's control terminal. If it clears, the fault is in the solenoid; if it does not, the fault is between the connector and the module. Same logic, different instrument.

As for what actually shorts, the exhaust side of the cylinder head is the governing factor. The harness runs across a hot, grounded aluminium casting with exhaust plumbing nearby, insulation there hardens and cracks far sooner than it does elsewhere on the engine, and once it splits the conductor is resting on grounded metal. Missing or badly refitted heat shielding accelerates the whole process considerably.

The engine remains driveable. The exhaust phaser parks in its default position, power is largely unaffected, and the practical costs are a small economy penalty and a rise in oxides of nitrogen. There is no urgency mechanically, though a circuit shorted to ground is stressing a module driver and is not worth leaving indefinitely.

Common causes

Control wire shorted to ground where insulation has cracked from exhaust-side heat
Exhaust valve control solenoid with an internally shorted winding
Shared supply, ground or splice fault when both banks report low together
Harness crushed or pinched under a bracket, heat shield or fastener during previous service
Missing or incorrectly refitted heat shielding leaving the harness exposed to radiant heat
Corrosion or moisture inside the connector creating a conductive path to ground
Incorrect replacement solenoid drawing more current than the module's driver expects
Harness chafed against a machined casting edge on the exhaust side of the cylinder head
Failed low-side driver inside the module holding its own output down

Symptoms

Check engine light on with P0079 stored
Little or no change in how the vehicle drives
Slightly rough idle on engines that use exhaust phasing for idle stability
Small reduction in fuel economy at part load
Failed emissions test on oxides of nitrogen
Bank 2 exhaust solenoid code stored alongside it, indicating a shared circuit rather than two failed parts
Exhaust camshaft timing code on the same bank appearing as a consequence of the electrical fault
Solenoid output shown as disabled on a scan tool after the module protected itself from an overcurrent event

Diagnostic steps

1.Read all stored codes before testing anything, because the pattern is the fastest diagnostic tool available on this fault.
2.If the bank 2 exhaust solenoid has logged the same low circuit condition, stop and investigate the shared supply, ground, splice or module rather than either solenoid — two solenoids on opposite heads do not short on the same day.
3.If an exhaust camshaft timing code is also present on this bank, treat it as the consequence rather than the cause, repair the circuit first and only revisit the phaser if the timing code survives a proven-good circuit.
4.On an inline engine, where no bank 2 partner code can exist, disconnect the solenoid and check whether the low condition persists at the module's control terminal — clearing means the solenoid, persisting means the harness.
5.Measure resistance from the control terminal on the harness side to chassis ground with the connector disconnected and the ignition off.
6.Measure the solenoid's coil resistance across its terminals and compare with the manufacturer's specification.
7.Inspect the harness along the exhaust side of the cylinder head for hardened, cracked or split insulation, lifting the loom so the underside can be seen.
8.Confirm all heat shielding is present and correctly refitted, since exposed harness is the root cause behind most of these shorts and leaving it will destroy the repair.
9.Check the connector for moisture, corrosion and terminal condition, and use high-temperature parts for any repair in this location.
10.After repair, clear the codes, cycle the ignition off and on so any latched output is re-enabled, then run an actuation test and a warm-up drive before rechecking.

Repair cost

$100 – $650

Diagnosis is $90 to $180, and reading the full code set first is what keeps that number down. An exhaust valve control solenoid is $35 to $240 in parts with 0.4 to 2.5 hours of labour, so $140 to $560 fitted. Harness repair on the exhaust side is $130 to $340 because it needs high-temperature terminals and sleeving and often requires exhaust or shield removal to reach. Replacing missing heat shielding is $40 to $180. The costly mistake specific to this code is replacing both solenoids when both banks report low — that is $280 to $1,100 of parts and labour spent on a fault that lives in a shared feed, ground or splice, and both codes will still be there afterwards.

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DIY vs shop

This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.