Fault code P1850 – a step-by-step guide to diagnosing and fixing it

The meaning of error code P1850 – Transmission Transfer Case Contact Plate 'B' Circuit Failure

P1850: Causes, signs and repairs

Error code P1850 is displayed and the check engine light is on - what does this mean?

The DTC P1850 is a manufacturer-specific fault code that mainly occurs in General Motors vehicles and indicates problems with the transmission control unit. The OBD system detects irregularities in the electronic pressure control of the automatic transmission. This code can have different meanings for different manufacturers, which is why a precise diagnosis is important.

What causes can this error code have?

Defective transmission control unit (TCM/PCM)
Damaged wiring harness to the transmission control unit
Loose or corroded plug connections
Faulty transmission pressure sensors
Defective solenoid valves in the transmission valve body
Worn clutches or belts in the transmission
Low or contaminated transmission oil level
Internal gearbox damage or wear

What symptoms occur in parallel with fault code P1850?

Shifting problems: jerky or delayed gear changes
Transmission protection: Vehicle switches to emergency running mode
Engine performance: Reduced acceleration and driving performance
Shifting behavior: Transmission stalls in one gear
Vibrations: Unusual noises or vibrations when changing gear
Starting problems: Vehicle is difficult to start

How can the problem with error code P1850 be rectified?

The repair requires a systematic approach, as various components can be affected.
Check the transmission oil level and quality, change if necessary and bring to the correct level
Check all electrical connections to the transmission control unit for corrosion and tight fit and clean them
Read out transmission control unit with diagnostic device and have it replaced if defective
Test transmission pressure sensors individually and replace defective sensors
Check solenoid valves in the transmission valve body and replace the entire valve body if necessary
Have internal transmission components checked by a specialist workshop and have worn parts replaced

FAQ - Frequently asked questions about DTC P1850

Can I continue driving with error code P1850?

Short distances are possible, but you should visit a workshop as soon as possible. The code P1850 can lead to serious damage to the transmission if it is ignored.

How much does it cost to repair error code P1850?

The costs vary depending on the cause: oil change 150-300€, sensors 200-500€, control unit 800-1500€, complete transmission repair 2000-4000€.

Is error code P1850 a serious problem?

Yes, this trouble code indicates serious transmission problems. Without repair, costly consequential damage to the automatic transmission can occur.

How can I delete error code P1850?

After the repair, the code can be deleted with an OBD diagnostic device. However, it will return if the problem has not been rectified.

What tools do I need to diagnose P1850?

An EOBD diagnostic tool, multimeters for electrical measurements and special transmission pressure gauges are required.

Can I repair fault code P1850 myself?

Simple checks such as oil level are possible, but most repairs require the expertise and special tools of a transmission workshop.

Vehicles in which error code P1850 occurs most frequently

Error code P1850 is a manufacturer-specific DTC and can indicate various transmission and control problems, but is most common in the following vehicles:

General Motors: Chevrolet Silverado, GMC Sierra, Cadillac Escalade, Chevrolet Tahoe, GMC Yukon (1999-2010)
Chevrolet: Suburban, Avalanche, Express Van, Corvette (2000-2012)
GMC: Savana, Canyon, Envoy (2001-2009)
Cadillac: DeVille, DTS, STS (2000-2011)
Buick: LeSabre, Park Avenue, Lucerne (1999-2009)
Pontiac: Grand Prix, Bonneville (2000-2008)
Oldsmobile: Aurora, Intrigue (1999-2004)

If the code P1850 occurs in your vehicle, a quick diagnosis is important, as transmission problems can quickly lead to costly repairs. Especially with older GM vehicles, you should take the fault code seriously and visit a specialized workshop as soon as possible. Early rectification can prevent expensive consequential damage to the automatic transmission.

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