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Home / DTC / P0848 — Trans Fluid Press Sensor/Switch B Circuit High

P0848 — Trans Fluid Press Sensor/Switch B Circuit High

Detailed page for trouble code P0848.

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11,925generic
22,981specific
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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
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Page language: EN

Causes

  • Short to battery (12V) on the sensor signal circuit
  • Faulty transmission fluid pressure sensor/switch B
  • Open or corroded ground or reference circuit at sensor
  • Damaged/deteriorated wiring or connector (chafing, pinched, corrosion, water intrusion)
  • Poor connector pin contact or terminal corrosion
  • Faulty transmission control module (TCM) or PCM input stage

Symptoms

  • Malfunction Indicator Lamp (MIL) / transmission warning lamp illuminated
  • Transmission may enter limp mode or limited gear selection
  • Harsh, delayed or abnormal shifting
  • Erratic transmission behavior or torque converter lockup issues
  • Possible stored related transmission fault codes

What to check

  • Retrieve DTCs and freeze frame data with a capable scan tool; note occurrence and any secondary codes
  • Visually inspect sensor connector and wiring for damage, corrosion, stretched pins, or signs of water intrusion
  • Backprobe sensor connector and measure signal voltage with ignition ON / engine OFF and during engine running / gear changes
  • Check reference voltage (typically 5V) and ground at the sensor harness with a DMM
  • Measure continuity/resistance between sensor ground and chassis ground and between sensor signal and TCM pin
  • Wiggle harness and connector while monitoring live data for intermittent changes

Signal parameters

  • Typical sensor type: analog voltage pressure sensor (0–5 V range)
  • Expected idle/low pressure: ~0.5–1.0 V (vehicle dependent)
  • Expected high pressure: ~3.0–4.5 V under load (vehicle dependent)
  • Reference supply: ~5 V from TCM/ECU
  • Open circuit or short-to-voltage may read near battery voltage or frozen high value

Diagnostic algorithm

  1. Confirm code and record freeze frame/live data. Check for multiple occurrences and related transmission codes.
  2. Perform a careful visual inspection of the sensor, connector and wiring harness routing for abrasion, pin damage, corrosion or evidence of fluid ingress.
  3. With the connector connected, backprobe the signal, reference and ground pins. Verify reference voltage (~5V), good ground and signal voltage. Note whether signal is stuck high.
  4. If reference or ground is missing or out of range, trace and repair the supply/ground (check connectors and TCM pin).
  5. If reference and ground are correct but signal is high, disconnect the sensor and measure harness signal to TCM for short to battery (continuity to power).
  6. Measure resistance between sensor signal and ground; compare to manufacturer values if available. If sensor wiring checks out, substitute a known good sensor or bench test sensor if possible.
  7. If wiring and sensor pass tests but code persists, check for intermittent faults (wiggle test while monitoring) and inspect TCM connectors and grounds. Consider TCM input stage failure if harness and sensor are confirmed good.
  8. After any repair or replacement, clear codes, re-run diagnostic checks and perform a road test while monitoring live pressure sensor data to confirm proper operation.

Likely causes

  • Damaged wiring/connector shorted to battery or power feed
  • Failed pressure sensor/switch B
  • Corroded connector or poor ground at sensor
  • Internal TCM/ECU fault (less common)

Fault status

⚠️ Status
Transmission Fluid Pressure Sensor/Switch B Circuit High — The transmission control module detected a higher‑than‑expected voltage from the fluid pressure sensor/switch B circuit, indicating a possible short to battery, sensor failure, or wiring/connector issue.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-3.0 hours

Similar codes

P0845 P0846 P0847 P0849 P0700
856

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