P2742 — Transmission Fluid Temperature Sensor "B" Circuit Low

P2742 — Transmission Fluid Temperature Sensor "B" Circuit Low. A fault in the automatic transmission control. Short, gentle driving to a shop is usually possible. Typical causes: failed shift or pressure control solenoid, faulty transmission speed sensor, internal mechanical wear (clutches, torque converter).

powertrain (engine/transmission)

Is it safe to drive?

Drive with caution Drive only if the transmission still shifts predictably, and avoid highway speeds. Driving with slipping or limp mode accelerates internal wear — every kilometre can add to the final repair bill.

How to diagnose with an OBD scanner

  1. Read the code and freeze frame Connect an OBD2 scanner, confirm P2742 is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
  2. Check for companion codes and TSBs Related codes often reveal the real root cause. Also check manufacturer technical service bulletins (TSB) for your make and model — many P0xxx issues have factory fixes or software updates. Search by VIN on the manufacturer site or nhtsa.gov.
  3. Inspect wiring and connectors Visually inspect the wiring harness and connectors related to the automatic transmission control for damage, corrosion, chafing or poor contact.
  4. Subsystem check Check for supply voltage at the transmission fluid temperature sensor "B" connector first; then measure resistance from the signal wire to ground — near-zero ohms confirms a short to ground in the harness.
  5. Subsystem check Check transmission fluid level and condition — dark, burnt fluid points to internal wear.
  6. Subsystem check Read transmission-specific codes and live data (solenoid states, input/output speed) with a capable scanner.
  7. Verify the repair Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm P2742 does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for P2742 (parts and labor, USD, independent shop rates): Replace a shift solenoid: $300–$800; Transmission fluid service: $150–$350; Transmission rebuild or replacement: $2,500–$5,500; Valve body repair or replacement: $700–$1,500. Overall, fixing P2742 usually costs between $150 and $5,500. An accurate diagnosis before buying parts saves money — the most expensive scenario is rarely the first one to check.

Common questions

Will P2742 clear itself?

Sometimes P2742 clears after a few drive cycles if the fault was intermittent — for example a loose connector or a tank of bad fuel. The underlying cause usually remains, so the code tends to return. Clear it once; if it comes back, diagnose rather than erase it repeatedly.

What does OBD2 code P2742 mean?

P2742 — Transmission Fluid Temperature Sensor "B" Circuit Low. A fault in the automatic transmission control. Short, gentle driving to a shop is usually possible. Typical causes: failed shift or pressure control solenoid, faulty transmission speed sensor, internal mechanical wear (clutches, torque converter).

How much does it cost to fix P2742?

Replace a shift solenoid — $300–$800; Transmission fluid service — $150–$350; Transmission rebuild or replacement — $2,500–$5,500; Valve body repair or replacement — $700–$1,500. Exact cost depends on the root cause, your vehicle and local labor rates — a proper diagnosis is the cheapest first step.

What are the symptoms of P2742?

Drivers most often notice: no movement in severe cases, slipping between gears, shuddering at highway speed, harsh or delayed shifting.

How do I diagnose P2742 myself?

Start with a scan: confirm P2742, save the freeze frame and note any companion codes. Then inspect the wiring and connectors related to the transmission fluid temperature sensor "B", and verify the suspect component against live data before buying parts.

What does P2742 mean?

Seeing P2742 on your scanner? The control unit has caught the automatic transmission control operating outside its calibrated window. The formal description is “Transmission Fluid Temperature Sensor "B" Circuit Low”, and the code is grouped under powertrain (engine/transmission) faults.

“Circuit low” means the voltage on the transmission fluid temperature sensor "B" circuit stays below the expected minimum — close to ground. The usual physical reasons are a short to ground, a chafed wire touching metal, a missing supply voltage, or a failed component dragging the signal down.

To set P2742, the control module compares live readings of the automatic transmission control against calibrated limits, usually over several drive cycles. Alongside the code it stores a freeze frame — a snapshot of rpm, load, coolant temperature and vehicle speed at the moment of failure. Reading that snapshot first saves diagnostic time.

Common symptoms of P2742

  • no movement in severe cases
  • slipping between gears
  • shuddering at highway speed
  • harsh or delayed shifting
  • transmission stuck in one gear (limp mode)
  • Check Engine or transmission warning light on

What causes P2742?

  • missing supply voltage to the transmission fluid temperature sensor "B"
  • signal wire shorted to ground (chafed insulation)
  • failed transmission fluid temperature sensor "B" pulling the signal low
  • wiring or connector faults in the valve body harness
  • valve body wear
  • low or degraded transmission fluid
  • faulty transmission speed sensor

How to diagnose P2742

  1. Connect an OBD2 scanner, confirm P2742 is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
  2. Related codes often reveal the real root cause. Also check manufacturer technical service bulletins (TSB) for your make and model — many P0xxx issues have factory fixes or software updates. Search by VIN on the manufacturer site or nhtsa.gov.
  3. Visually inspect the wiring harness and connectors related to the automatic transmission control for damage, corrosion, chafing or poor contact.
  4. Check for supply voltage at the transmission fluid temperature sensor "B" connector first; then measure resistance from the signal wire to ground — near-zero ohms confirms a short to ground in the harness.
  5. Check transmission fluid level and condition — dark, burnt fluid points to internal wear.
  6. Read transmission-specific codes and live data (solenoid states, input/output speed) with a capable scanner.
  7. Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm P2742 does not return.

How to fix P2742

Start with the cheapest and most common causes before replacing expensive parts:

  • Replace a shift solenoid — $300–$800
  • Transmission fluid service — $150–$350
  • Transmission rebuild or replacement — $2,500–$5,500
  • Valve body repair or replacement — $700–$1,500

How much does it cost to fix P2742?

Repair cost depends on which component actually failed. Typical scenarios for P2742 (parts and labor, USD, independent shop rates):

  • Replace a shift solenoid: $300–$800
  • Transmission fluid service: $150–$350
  • Transmission rebuild or replacement: $2,500–$5,500
  • Valve body repair or replacement: $700–$1,500

Overall, fixing P2742 usually costs between $150 and $5,500. An accurate diagnosis before buying parts saves money — the most expensive scenario is rarely the first one to check.

Can you drive with P2742?

Drive only if the transmission still shifts predictably, and avoid highway speeds. Driving with slipping or limp mode accelerates internal wear — every kilometre can add to the final repair bill.

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