How can I tell whether the sensor or the wiring is at fault without special tools?

Use the second bank as your reference. Leave the vehicle overnight, then read both exhaust temperature values before starting it. Two sensors sitting in the same cold engine bay should report nearly the same number. If bank 1 is sensible and bank 2 is at the bottom of its range, the bank 2 circuit is faulty. Then unplug the bank 2 sensor: if the reading stays down with nothing connected, the wiring is shorted and the sensor is innocent.

Why does one bank's sensor stop the vehicle from regenerating at all?

Because there is only one particulate filter and both banks exhaust into it. Soot load is a single number for that filter, and a regeneration is a deliberately hot burn that has to be supervised. With one temperature input untrustworthy the module has an incomplete picture of what is happening inside the exhaust, and commanding a hot burn blind risks damaging the very components it is trying to clean. It declines. So the practical effect of a half-blind system is the same as a fully blind one.

Where should I start looking for a chafed wire?

In the middle, not at the ends. The bank 2 sensor lead is unusual in that it has to travel across the engine bay to reach the main harness, and that crossing section is longer, spans more clamp points and passes more hot and moving hardware than any part of the bank 1 circuit. Follow it with your hands and look specifically at every point where it is secured, since a wire that flexes against a fixed anchor is where insulation gives out first.

Is it worth replacing both exhaust temperature sensors at the same time?

It depends entirely on access. Where both sensors are easy to reach and the vehicle has high mileage, doing the pair is reasonable preventive work since they age at the same rate under the same conditions. Where the bank 2 sensor requires removing the intake, the calculation changes completely — the labor is the expense and you would be paying it twice, or paying it once and replacing a bank 1 sensor that has shown no sign of trouble. Confirm which sensor is actually faulty first and let access decide the rest.

OBD-II trouble code

P0548: Exhaust Gas Temperature Sensor Circuit Low Bank 2 Sensor 1

Signal voltage below the acceptable floor on the second bank's exhaust temperature sensor. The useful thing about a bank 2 fault is that the vehicle carries a matching sensor on the other side, which turns a specification lookup into a simple side-by-side comparison.

Medium severityPowertrainExhaust / AftertreatmentDrivable short-term

Quick facts

System: Powertrain
Category: Exhaust / Aftertreatment
Severity: Medium severity
Drivable: Usually safe to drive short-term
Repair cost range: $150 – $1,200
DIY difficulty: Advanced DIY

What does P0548 mean?

This code combines two separate pieces of information and both are worth reading carefully. The low half tells you the circuit is being dragged down toward ground — an unintended conductive path somewhere between the module and the sensor tip. The bank 2 half tells you which of the vehicle's exhaust temperature circuits is doing it, and on a two-bank engine that turns out to be the more useful half.

Here is why. Diagnosing a single sensor usually means finding a resistance-versus-temperature table for the exact part and interpreting a number against it. On a two-bank engine you do not have to. There is a second sensor of the same type, on the same engine, breathing the same ambient air, and after an overnight soak both should report essentially the same temperature within a few degrees of each other. If bank 1 reads sixty degrees and bank 2 reads the bottom of the scale, you have proved a circuit fault without knowing a single specification value. That cross-check is the fastest and most reliable first test available on this code and it does not exist for the bank 1 codes, which have nothing to be compared against.

The physical reason bank 2 low-side faults happen at all comes down to how the harness has to get there. A bank 1 sensor generally has a short run to the nearest harness junction. The bank 2 branch, particularly on transverse V engines, has to cross the engine bay — over the top of the engine, around behind it, or down and under — to reach the same junction. That extra length passes more heat sources, spans more clamp points, and often includes an inline connector that bank 1 does not have. Every one of those is a place where insulation can wear through and put the conductor onto a ground. Statistically, when a bank 2 circuit is shorted low, the short is more likely to be somewhere in the middle of that crossing run than at either end, which is the opposite of where most people start looking.

The consequence is global rather than local, and this catches owners out. Both banks feed a single particulate filter, and soot load is measured for that filter as a whole. A module missing a trustworthy temperature from either bank will not command a regeneration, because it cannot verify what is happening to the hardware it is trying to protect. So a fault affecting half the exhaust stops the regeneration strategy for the entire vehicle, and soot accumulates at the normal rate with nothing clearing it. The sensor is not the expensive part of this problem; the filter downstream is.

Common causes

Signal conductor shorted to ground where the bank 2 branch crosses the engine bay and contacts a bracket, pipe or the block
Insulation worn through at a clamp point on the long bank 2 harness run
Internally shorted sensing element in the bank 2 sensor
Water and corrosion bridging terminals in an inline connector on the bank 2 branch, which is often the only such connector in the circuit
Signal and ground conductors crushed together inside a grommet or pass-through
Harness pinched or trapped during a previous intake manifold or rear-bank service
Incorrect replacement sensor with a resistance curve that never reaches the module's expected window
Module-side pull-down fault, which is uncommon and should be the last thing considered

Symptoms

Check engine light with normal driveability for the first days or weeks
Bank 2 exhaust temperature reading at the bottom of the scale while bank 1 tracks normally
Regeneration cycles that never complete, with the vehicle covering hundreds of miles between successful burns
Soot load climbing steadily and eventually triggering restriction warnings
Reduced power appearing later, once the filter has loaded far enough for the module to act
Fault that comes and goes with engine load, consistent with a short that closes as the engine rocks on its mounts
Oil level creeping upward on applications that abort regenerations after starting them
Additional aftertreatment codes accumulating over time as the original fault goes unresolved

Diagnostic steps

1.Put bank 1 and bank 2 exhaust temperatures side by side in live data on a cold engine. Two sensors in the same still air should agree closely, so a large split between them confirms an electrical fault immediately and tells you which side to work on without needing a resistance chart.
2.Disconnect the bank 2 sensor and watch what the circuit does. If the low reading persists with the sensor removed from the circuit, the short is in the harness. If the reading releases to the opposite extreme, the fault is inside the sensor. This single step splits the job in half before any wire is touched.
3.Measure resistance from the disconnected harness signal pin to ground. Any low value is a confirmed short and locates the work in the wiring, not the component.
4.Trace the crossing section of the bank 2 branch specifically. This is the length bank 1 does not have — the part that runs over, behind or under the engine to reach the main harness — and it is where the chafe usually is. Check where it passes brackets, coolant pipes and the transmission bellhousing area.
5.Open any inline connector on that branch and inspect the terminals. Bank 2 circuits often include a joint that bank 1 does not, and a joint sitting low in the engine bay collects water. Corrosion bridging two adjacent terminals produces exactly this code.
6.Check the regeneration history and soot load before finishing. This code suppresses regeneration for the whole vehicle rather than for one bank, so the filter may need a forced burn once the circuit is repaired, and finding that out now is better than finding out on the road.

Repair cost

$150 – $1,200

A short traced to the crossing section of the bank 2 harness and repaired with proper heat-resistant sleeving is typically $180 to $450, most of which is the time spent finding it rather than the materials. Sensor replacement is where the bank matters: $200 to $450 where the sensor is reachable, and up to $1,200 on transverse V engines where the intake has to come off to get at the rear bank. Budget an additional $150 to $350 for a forced regeneration if the filter has loaded while the code was active, and note that a filter allowed to plug completely runs $1,500 to $4,000 — which is the number that should drive the timing of this repair.

Estimate your repair

Run the numbers for your vehicle

Open the Repair Cost Estimator with exhaust gas temperature (egt) sensor replacement preselected. Adjust labor rate and vehicle category to fit your situation.

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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.