U0291 — Lost Communication With Gear Shift Control Module "B"

OBD2 code U0291 flags a problem with the automatic transmission control (lost communication with gear shift control module "B"). Short, gentle driving to a shop is usually possible. Common culprits: internal mechanical wear (clutches, torque converter), valve body wear, faulty transmission speed sensor.

vehicle network

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

Read the code and freeze frame Connect an OBD2 scanner, confirm U0291 is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
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 U0xxx issues have factory fixes or software updates. Search by VIN on the manufacturer site or nhtsa.gov.
Inspect wiring and connectors Visually inspect the wiring harness and connectors related to the automatic transmission control for damage, corrosion, chafing or poor contact.
Subsystem check Check transmission fluid level and condition — dark, burnt fluid points to internal wear.
Subsystem check Read transmission-specific codes and live data (solenoid states, input/output speed) with a capable scanner.
Verify the repair Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm U0291 does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for U0291 (parts and labor, USD, independent shop rates): Transmission fluid service: $150–$350; Transmission rebuild or replacement: $2,500–$5,500; Valve body repair or replacement: $700–$1,500; Replace a shift solenoid: $300–$800. Overall, fixing U0291 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 U0291 clear itself?

Sometimes U0291 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 is the most common cause of U0291?

The most common causes are: internal mechanical wear (clutches, torque converter), valve body wear, faulty transmission speed sensor.

Is it safe to drive with U0291?

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 do I diagnose U0291 myself?

Start with a scan: confirm U0291, save the freeze frame and note any companion codes. Then inspect the wiring and connectors related to the automatic transmission control, and verify the suspect component against live data before buying parts.

What are the symptoms of U0291?

Drivers most often notice: Check Engine or transmission warning light on, slipping between gears, harsh or delayed shifting, no movement in severe cases.

What does U0291 mean?

Behind U0291 is a specific failure in the automatic transmission control: lost communication with gear shift control module "B". The onboard computer stores it in the vehicle network group after verifying the fault over repeated checks.

This code does not appear from a single bad reading: the module must see the fault condition repeat under defined operating conditions before it turns on the warning light. The freeze frame captured with U0291 — engine load, rpm, temperature, speed — tells you exactly when the problem occurs, so reproduce those conditions when testing.

What causes U0291?

faulty transmission speed sensor
internal mechanical wear (clutches, torque converter)
valve body wear
failed shift or pressure control solenoid
low or degraded transmission fluid
wiring or connector faults in the valve body harness

Common symptoms of U0291

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

How to diagnose U0291

Connect an OBD2 scanner, confirm U0291 is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
Related codes often reveal the real root cause. Also check manufacturer technical service bulletins (TSB) for your make and model — many U0xxx issues have factory fixes or software updates. Search by VIN on the manufacturer site or nhtsa.gov.
Visually inspect the wiring harness and connectors related to the automatic transmission control for damage, corrosion, chafing or poor contact.
Check transmission fluid level and condition — dark, burnt fluid points to internal wear.
Read transmission-specific codes and live data (solenoid states, input/output speed) with a capable scanner.
Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm U0291 does not return.

How to fix U0291

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

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

How much does it cost to fix U0291?

Repair cost depends on which component actually failed. Typical scenarios for U0291 (parts and labor, USD, independent shop rates):

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

Overall, fixing U0291 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 U0291?