OBD-II Diagnostic Trouble Code
P0848 — Transmission Fluid Pressure Sensor/Switch B Circuit
P0848 indicates a fault in the transmission fluid pressure sensor or switch B circuit. The TCM sees a signal that is out of range or inconsistent with the commanded gear state for pressure switch B.
Severity 3/5
Truck-relevant
Service this week
Severity
Service this week
Transmission Fluid Pressure Sensor/Switch B Circuit
Code
P0848
Category
Powertrain
Subsystem
Transmission
Truck-relevant
Yes
What this means for truckers
P0848 (Transmission Fluid Pressure Sensor B Circuit) — secondary pressure sensor on multi-sensor transmissions. Diagnose with scan tool — compare to factory spec pressure.
Before you replace parts — try this first
P0848 on the Transmission system is most often wiring or connector fault — not a dead part. On commercial diesels especially, work these in order before spending money on parts:
- Confirm the symptoms. Match what your truck is doing to the Symptoms section below. If the code is set but the symptoms are not there, clear the code and re-test after a drive cycle — it may not return.
- Clean and dry the sensor connector. Water, road salt, or oil seeping into a connector is the #1 fake sensor failure. Disconnect, look for green corrosion or moisture, spray with electrical contact cleaner, dry, reseat. Many faults clear here for $0.
- Inspect the wiring harness. Trace the wire from the sensor toward the ECM — look for chafing against the engine block, melted insulation near the turbo or exhaust, or pinch points where a clamp has rubbed through.
- Test the sensor before swapping it. Most Common Causes (below) list the expected voltage or resistance range — a $20 multimeter saves a $300 sensor swap that does not fix the problem.
- Only then, replace the part. Use the OEM or a tier-1 aftermarket. Cheap sensors throw the same code in two weeks.
Symptoms
Erratic shifting, wrong gear indications, harsh shifts and possible limp-home mode. Warning light on.
Common causes
- CommonWiring or connector fault ($120–$450)
- CommonFailed pressure switch B or switch manifold ($250–$800)
- OccasionalActual hydraulic pressure problem in the monitored circuit ($400–$2800)
- RareTCM fault ($900–$2500)
How to fix
Inspect wiring and connector
When to use: First check
Monitor pressure switch states on a scan tool while shifting
When to use: To see if the switch reads correctly
Perform a mechanical pressure test
When to use: To rule out actual pressure loss
Replace pressure switch or manifold
When to use: When the switch fails testing
Affects most
No specific vehicle pattern found in our complaint database. This code can appear on any vehicle that supports OBD-II diagnostics.
Related
Frequently Asked Questions
Can I drive with code P0848?
P0848 is severity 3 — plan service within a few days. Performance is likely degraded already (you may feel reduced power, harsher shifts, or slightly worse fuel economy). Continuing to drive risks additional damage to adjacent components.
How much does it cost to fix P0848 on a commercial truck?
Total repair cost ranges $120–$2800 depending on the root cause. The cheapest fix is usually the first one listed below — Wiring or connector fault — which is also the most common. On commercial trucks the cost is usually higher than passenger vehicles due to part availability and shop labor rates ($120–185/hour at most truck shops, vs $90–130 at general auto shops). DIY-capable fixes (sensors, hoses, filters) are at the low end; major component replacements (turbo actuator, high-pressure fuel pump, transmission solenoid pack) are at the high end. Always diagnose with a scan tool BEFORE replacing parts — guessing wrong on a $1,500 turbo actuator when the actual issue was a $30 boost hose is a common expensive mistake.
Will P0848 fail a DOT inspection?
P0848 typically doesn't fail an inspection on its own. Inspectors focus on safety items (brakes, steering, tires, lights, HOS). Transmission codes only become an issue if the truck has shifting problems severe enough to qualify as 'mechanical fitness' OOS. Fix to prevent escalation.
What's the difference between P0848 and related codes?
P0848 is closely related to: P0867 (Transmission Fluid Pressure), P0868 (Transmission Fluid Pressure Low), P0869 (Transmission Fluid Pressure High). These codes share the same subsystem (transmission) and often appear together. If you see this code, scan for the full code list — fixing the root cause usually clears multiple companion codes at once. If only P0848 is set without the companions, the issue is more isolated.
How do I prevent P0848 from coming back after a repair?
For P0848 (Transmission Fluid Pressure Sensor/Switch B Circuit), prevention centers on the transmission system. Service transmission fluid at the OEM interval (typically 150K–250K miles for HD autos). Don't skip the magnet/strainer inspection. After repair, perform an adaptive shift relearn with a scan tool (or drive 40+ miles for adaptive ECMs to relearn naturally).