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1999 GMC Sonoma Problems

RepairPal has identified the most common problems with the 1999 GMC Sonoma based on complaints from actual vehicle owners. We'll tell you what the problem is and what it'll take to fix it.

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17
Known Problems

The fuel pump may fail causing the engine to stall and not restart. Our technicians recommend replacing the fuel filter every 30,000 miles to help prevent undue strain on the fuel pump.

The distributor may develop internal faults. This can cause a rough running engine or stalling condition and the Check Engine Light may or may not illuminate. The distributor should be overhauled or replaced to correct this concern.

The heater core under the right side of the dashboard may leak engine coolant which can puddle on the passenger front floor. The loss of coolant may cause an engine overheating condition. Our technicians tell us that removal of the dash board is necessary to replace the heater on these vehicles.

The 1998-2002 GMC Sonoma has a known issue with the air pump check valve which causes illumination of the check engine light. There are no notable symptoms, but the vehicle will not pass state inspection or smog testing. 

When the valve fails, it sticks closed, and the computer sets the code P1416. Replacement of the check valve is the only fix, as the valve is not serviceable. 

This page can provide more information about the air pump check valve. 

The headlight switch used on the GMC Sonoma is known to fail through normal operation. Since the headlight switch is also integrated into the interior lights, a malfunctioning switch can cause issues with interior lights as well.

  • Symptoms of a failed headlight switch include:
  • Headlights and taillights failing to turn on or off
  • Interior lights flicker, or fail to turn on or off
  • Gauge cluster lighting off or flickering with headlights on
  • Parking light malfunctions  

This issue is well known with General Motors Trucks and SUVs, and is solved by testing and, if needed, replacing the headlight/dimmer switch. Bad grounding wires at the tail-lights, and dirty/corroded tow package wires can also lead to some of these issues. 

A fluid leak may develop from the transmission output shaft seal. This leak may cause the transmission mount to become oil soaked and require replacement of the mount along with the leak repair.

Vehicles equipped whit a 4 speed automatic transmission may develop a harsh 1-2 shift and/or illumination of the Check Engine Light with code P1870 stored. This can be caused by wear of the bore for the TCC isolator and regulator valves in the valve body. This condition does not commonly occur until the transmission reaches normal operating temperature. If the valve body is worn, replacement will be necessary to correct this concern.

A Loose or worn gas cap may cause Check Engine Light to illuminate.

The serpentine belt tensioner can fail; it may become noisy and/or the belt may jump off. Replacement of the failed tensioner will be necessary.

The spark plug wire rubber boots may get soaked with oil, causing a misfire or rough idle.

GM recommends replacing the engine coolant at 100,000 miles; however, our technicians tell us that the coolant may become contaminated and require a complete cooling system flush every 60,000 to 70,000 miles.

Our technicians highly recommend that the transmission is serviced every 30,000 miles to avoid problems and maintain optimal operating order.

The alternator may fail, causing a "no charge" condition. An internal bearing may also fail and cause an abnormal noise. If the vehicle is driven too long with a failed bearing, the alternator may stop turning, which can cause the serpentine belt to break or the engine to stall and not turn over.

Brake fluid can become dirty and may cause problems in the brake system; it should be flushed every 60,000 miles.