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Home / DTC / P0848 — Transmission Fluid Pressure Sensor/Switch B Circuit High

P0848 — Transmission Fluid Pressure Sensor/Switch B Circuit High

Detailed page for trouble code P0848.

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59brands
11,914generic
22,491specific
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P0848

Generic P — Powertrain

Transmission Fluid Pressure Sensor/Switch B Circuit High

Brand: Generic
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Short to battery or 5V reference on the sensor signal wire
  • Open or corroded ground on the sensor circuit
  • Damaged, chafed, or disconnected wiring or connector
  • Failed transmission fluid pressure sensor/switch B
  • Poor PCM/ECM connector or internal module fault (less common)
  • Contaminated or low transmission fluid producing abnormal sensor behavior (less common)

Symptoms

  • Transmission may enter limp mode or fail-safe shift strategy
  • Check Engine/Transmission warning light illuminated
  • Harsh, delayed, or erratic shifting (may be intermittent)
  • Stored freeze-frame or live-data showing abnormally high pressure signal voltage
  • No obvious mechanical noise related to the transmission (if purely electrical)

What to check

  • Read freeze-frame and live-data values with a scan tool; confirm P0848 is active or historical
  • Visually inspect sensor connector and wiring for damage, corrosion, or fluid contamination
  • Backprobe the sensor connector and measure signal voltage with key ON, engine OFF
  • Check reference voltage (usually ~5V) and ground at the sensor harness
  • Measure continuity and resistance between sensor ground and battery negative
  • Check for shorts to battery voltage on the signal wire (voltage present when it should be low)

Signal parameters

  • Typical reference voltage to sensor: ~5.0 V (key ON, engine OFF)
  • Expected signal voltage range (depends on pressure): ~0.5 V to ~4.5 V during operation
  • Circuit High condition: signal voltage near reference/battery (typically >4.5–4.8 V)
  • Ground at sensor should be near 0 V (low resistance to vehicle ground)
  • If sensor is a switch type: expected closed/open states; verify per vehicle spec

Diagnostic algorithm

  1. Verify the DTC with a scan tool. Record freeze-frame and live-data for the pressure B signal.
  2. Visually inspect the sensor, connector, and harness for damage, corrosion, or fluid intrusion. Repair any obvious wiring/connectors.
  3. With ignition ON (engine OFF), backprobe the sensor connector: • Measure reference voltage (should be ≈5V). • Measure signal voltage — if it reads ≈5V and should not, suspect short to 5V or failed sensor.
  4. Check sensor ground: measure resistance from sensor ground pin to battery negative. High resistance indicates poor ground that must be fixed.
  5. Perform a wiggle test on the harness while monitoring live-data and voltage to find intermittent shorts/opens.
  6. If wiring appears intact, disconnect sensor and measure signal circuit for short to battery (voltage present with sensor disconnected). If voltage disappears when disconnected, suspect sensor internal short.
  7. If possible, bench-test or replace the pressure sensor/switch B with a known-good unit and recheck live-data.
  8. If replacement sensor does not clear the issue, trace and repair harness to the PCM. Check PCM connector pins for corrosion or damage.
  9. After repair or replacement, clear codes and perform a road test to confirm the fault does not recur. Re-scan and verify proper signal behavior across operating conditions.
  10. If all harness and sensor tests are good and the fault persists, consider PCM diagnostic/repair per manufacturer procedures.

Likely causes

  • Wiring short to a fused 5V reference (most likely when signal reads ~5V)
  • Failed pressure sensor/switch B
  • Poor connector pin contact or corrosion at sensor harness
  • Open ground or high-resistance ground in the harness
  • Intermittent harness damage causing intermittent high voltage

Fault status

⚠️ Status
Transmission fluid pressure sensor/switch B circuit reporting excessively high signal voltage to PCM (possible short to battery or faulty sensor).
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-3.0 hours
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Code

P0848

MERCEDES-BENZ P — Powertrain

Trans Fluid Press Sensor/Switch B Circuit High

Brand: MERCEDES-BENZ
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Short to battery or 5V reference on the sensor signal wire
  • Open or corroded ground on the sensor circuit
  • Damaged, chafed, or disconnected wiring or connector
  • Failed transmission fluid pressure sensor/switch B
  • Poor PCM/ECM connector or internal module fault (less common)
  • Contaminated or low transmission fluid producing abnormal sensor behavior (less common)

Symptoms

  • Transmission may enter limp mode or fail-safe shift strategy
  • Check Engine/Transmission warning light illuminated
  • Harsh, delayed, or erratic shifting (may be intermittent)
  • Stored freeze-frame or live-data showing abnormally high pressure signal voltage
  • No obvious mechanical noise related to the transmission (if purely electrical)

What to check

  • Read freeze-frame and live-data values with a scan tool; confirm P0848 is active or historical
  • Visually inspect sensor connector and wiring for damage, corrosion, or fluid contamination
  • Backprobe the sensor connector and measure signal voltage with key ON, engine OFF
  • Check reference voltage (usually ~5V) and ground at the sensor harness
  • Measure continuity and resistance between sensor ground and battery negative
  • Check for shorts to battery voltage on the signal wire (voltage present when it should be low)

Signal parameters

  • Typical reference voltage to sensor: ~5.0 V (key ON, engine OFF)
  • Expected signal voltage range (depends on pressure): ~0.5 V to ~4.5 V during operation
  • Circuit High condition: signal voltage near reference/battery (typically >4.5–4.8 V)
  • Ground at sensor should be near 0 V (low resistance to vehicle ground)
  • If sensor is a switch type: expected closed/open states; verify per vehicle spec

Diagnostic algorithm

  1. Verify the DTC with a scan tool. Record freeze-frame and live-data for the pressure B signal.
  2. Visually inspect the sensor, connector, and harness for damage, corrosion, or fluid intrusion. Repair any obvious wiring/connectors.
  3. With ignition ON (engine OFF), backprobe the sensor connector: • Measure reference voltage (should be ≈5V). • Measure signal voltage — if it reads ≈5V and should not, suspect short to 5V or failed sensor.
  4. Check sensor ground: measure resistance from sensor ground pin to battery negative. High resistance indicates poor ground that must be fixed.
  5. Perform a wiggle test on the harness while monitoring live-data and voltage to find intermittent shorts/opens.
  6. If wiring appears intact, disconnect sensor and measure signal circuit for short to battery (voltage present with sensor disconnected). If voltage disappears when disconnected, suspect sensor internal short.
  7. If possible, bench-test or replace the pressure sensor/switch B with a known-good unit and recheck live-data.
  8. If replacement sensor does not clear the issue, trace and repair harness to the PCM. Check PCM connector pins for corrosion or damage.
  9. After repair or replacement, clear codes and perform a road test to confirm the fault does not recur. Re-scan and verify proper signal behavior across operating conditions.
  10. If all harness and sensor tests are good and the fault persists, consider PCM diagnostic/repair per manufacturer procedures.

Likely causes

  • Wiring short to a fused 5V reference (most likely when signal reads ~5V)
  • Failed pressure sensor/switch B
  • Poor connector pin contact or corrosion at sensor harness
  • Open ground or high-resistance ground in the harness
  • Intermittent harness damage causing intermittent high voltage

Fault status

⚠️ Status
Transmission fluid pressure sensor/switch B circuit reporting excessively high signal voltage to PCM (possible short to battery or faulty sensor).
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-3.0 hours
856

Browse 856 MERCEDES-BENZ manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

MERCEDES-BENZ

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