1999 Pontiac Bonneville Problems

What owners report

Owners of the 1999 Bonneville report most often on a plastic upper intake manifold/plenum that warps, cracks or develops a hole, letting coolant into the engine and sometimes stalling or backfiring the car. A second recurring theme is fuel smell and leaks around the fuel pressure regulator and fuel lines, plus intermittent stalling that dealers often could not reproduce. Many of these complaints were filed between roughly 40,000 and 130,000 miles on cars that were already several years old.

1. 1
   Engine cooling

   Upper intake manifold/plenum failure (coolant leak)

   • 24 complaints (17%)
   • median 60,315 mi at 5.3 yrs old (21 state mileage)
   • 1 mention a crash, fire or injury
   • owner-quoted repair $1,023 (median of 10 quotes)
   • filed 2002–2014

   Owners describe the plastic upper intake manifold or plenum warping, cracking or burning a hole, which lets coolant into the engine. Symptoms reported include coolant loss without an obvious external leak, white smoke, hesitation or misfire, backfiring, and stalling that can end in a no-restart. Complaints say mechanics and dealers replaced the upper manifold and gaskets, in several cases more than once, and some report engine damage afterward. Several owners say they were told the part was a known repeat failure but that repairs were not covered once the car was out of warranty. Commonly reported between roughly 40,000 and 90,000 miles, with several owners noting repeat failures within a year or two of the first repair.

   What to check: Ask whether the upper intake manifold and gaskets have been replaced and when; check the coolant reservoir level over a few weeks and look for white exhaust smoke or a sweet smell. Look for a metal-sleeved replacement plenum, which some owners say was used as an improved part.

   2 excerpts from owner complaints in NHTSA records

   “1999 Bonneville; 58,000 miles; it had been stalling intermittently for several weeks -- especially during turns. Before I could take it to the dealer, the car loses power on hwy 63; fortunately, I was able to pull over. The mechanic reports engine has locked up because coolant has leaked into the engine due to a known problem by GM of coolant leaking into engine and thus destroying the engine. …”

   NHTSA complaint #10047511, filed 2003-11, 58,500 miles

   “Two intake manifold failures for my 1999 Pontiac Bonneville, 3.8 engine. First one was in january 2003. Now 15 months later, it has failed again after 35000 miles. The first time, repair costs were just over $800. Now I'm looking at a bill of $866. I have read the TSB and many other online complaints that I'm not the only one with this issue of recurring failures. Some have even reported fires in the engine compartments or complete engine failure.”

   NHTSA complaint #10116866, filed 2005-04, 46,000 miles
2. 2
   Fuel system

   Fuel smell and fuel pressure regulator leaks

   • 17 complaints (12%)
   • median 89,658 mi at 5.3 yrs old (11 state mileage)
   • 3 mention a crash, fire or injury
   • filed 2001–2011

   Complaints describe a gasoline smell, especially after parking in a garage, traced to the fuel pressure regulator, fuel lines or the fitting at the injector rail. Some owners report the regulator failing again after it was replaced under recall, and others say the dealer attributed the smell to deteriorated fuel lines instead. A few describe backfires or a fire under the hood around the time of the leak. Mostly reported between about 40,000 and 105,000 miles; several owners mention the regulator being replaced more than once.

   Recall 04V0900001 related service bulletin

   What to check: Ask whether recall 04V090000 (fuel pressure regulator) was performed and whether the regulator or fuel lines have been replaced since. Smell around the hood and under the rear of the car after it sits, and look for damp or cracked fuel lines.

   2 excerpts from owner complaints in NHTSA records

   “Noticed smell of gas when auto parked in garage..further investigation noted that fuel leaking from fuel line..took auto to dealer and dealer stated that both fuel lines have deteriorated, causing the leaks..while I have been familiar with fuel leaks from loose connections, I can not imagine how fuel lines can not been built to last.”

   NHTSA complaint #10161164, filed 2006-06, 80,551 miles

   “I've had major problems with my 99 Bonneville, costing me over $2,400. It started at 64,000 miles (6/26/02) with a backfire caused by a faulty fuel pressure regulator, which now has a service recall (a little too late); that cost me $300. A week later, the upper manifold plenum leaked causing the engine to flood and die; I spent over $500 on that little project (replacing the manifold and cleaning the engine). …”

   NHTSA complaint #10082225, filed 2004-07, 64,008 miles
3. 3
   Engine cooling

   Intermittent stalling and loss of power

   • 54 complaints (38%)
   • median 72,550 mi at 5.3 yrs old (24 state mileage)
   • 3 mention a crash, fire or injury
   • owner-quoted repair $1,200 (median of 7 quotes)
   • filed 1999–2016

   Owners report the engine cutting out at speed or while braking, turning or slowing, sometimes restarting right away and sometimes not. Several complaints say the dealer could not duplicate the problem or found nothing wrong, while others link the stall to the intake manifold or coolant entering the engine. A few describe losing power steering and power assist for the brakes at the same moment. Reported across a wide mileage range, from about 12,000 to 130,000 miles, often described as intermittent and hard to reproduce.

   What to check: Ask whether the stalling has been diagnosed and what was replaced (crank sensor, ignition switch, manifold). A long test drive that includes idling in traffic, turns and braking can help reveal an intermittent stall.

   2 excerpts from owner complaints in NHTSA records

   “Car stalled while driving home at night. No electrical power what so ever including emergency flashers. Nearly had an accident and had no way of indicating to other vehicles that I had a problem. No lights, no power steering, no brakes, no brake lights, no emergency flashers. After slowing down to appx. 25 MPH, power came back on. I shifted to neutral and was able to start the car and drive it home.”

   NHTSA complaint #10258626, filed 2009-02, 218,657 miles

   “I had to have the intake plenum replaced on my 99 Pontiac Bonneville...started with vehicle hesitating on take off, RPM's accelerating very high but MPH not catching up...vehicle then backfired and loss all power...had it towed to dealer...dealer said intake plenum was warped causing coolant to possibly leak into engine...GM would not cover under warranty which cost me $1000 to correct...vehicle was fine for a month or so and started doing it again. …”

   NHTSA complaint #10095676, filed 2004-10, 95,000 miles
4. 4
   Air bags

   Sudden airbag deployment without a crash

   • 8 complaints (6%)
   • median 114,292 mi at 6.9 yrs old (4 state mileage, few)
   • 5 mention a crash, fire or injury
   • filed 1999–2014

   Complaints describe the front airbag deploying while the car was being driven normally or while stopped, without an impact, and in one case with the airbag warning light off beforehand. Owners report minor injuries from the deployment and say the dealer found water inside an airbag module in one instance. The manufacturer was contacted in several cases, and owners say repairs were not covered. Reported from roughly 95,000 to 150,000 miles, on cars that were by then well out of warranty.

   1 related service bulletin

   What to check: Check that the airbag warning light comes on briefly at startup and then goes out, and ask whether any airbag module or sensor has been replaced. Look for signs of water intrusion in the footwells and under the dash.

   2 excerpts from owner complaints in NHTSA records

   “The driver owns a 1999 Pontiac Bonneville. The contact stated the driver was traveling approximately 65 MPH when the front drivers side air bag deployed involuntarily. The driver suffered minor injuries. The vehicle was taken to an authorized dealer where the contact was informed water was found within one of the air bag modules. The vehicle was not repaired. The manufacturer was notified, but offered no assistance. The failure mileage was 96,000. Updated 06/24/11”

   NHTSA complaint #10403963, filed 2011-06, 96,000 miles

   “The contact stated while traveling 35 MPH and getting off an exit from the highway, the front driver airbag deployed suddenly without warning. The vehicle did not impact any object on the road prior to the deployment. The driver did not lose control of the vehicle. The airbag warning light was not illuminated prior to the unwarranted deployment. The contact sustained minor lip injuries. The manufacturer was contacted and suggested that the vehicle needed to be inspected at an authorized dealership. …”

   NHTSA complaint #10167640, filed 2006-09, 131,585 miles
5. 5
   Brakes

   Brake pedal fade, fluid loss and line failure

   • 8 complaints (6%)
   • median 113,000 mi at 7.3 yrs old (3 state mileage, few)
   • 1 mention a crash, fire or injury
   • filed 1999–2009

   Owners report the brake pedal traveling farther than normal, the brake warning light coming on and brake fluid level dropping with no obvious puddle. Complaints describe grinding noise under braking, and in some cases a brake line failing so the car would not stop and had to be towed. Repairs involved replacing lines and hydraulic parts. Mostly reported between about 100,000 and 190,000 miles, on older, higher-mileage cars.

   What to check: Check brake fluid level and pedal feel, and have the hard brake lines inspected underneath for corrosion or wet spots before buying.

   2 excerpts from owner complaints in NHTSA records

   “Over the past few days noticed that the brake pedal was traveling much farther than normal. Since this is my wife 's car, and I do not drive it much,thought that the back shoes were low since they had not been replaced in awhile. Purchased a new set and planned on installing. However the next day noticed that the brake light warning came on and the brake fluid was low. Topped up and light went out. I thought that the low level was do to the worn shoes which would make the level go down. However the level continued to go down as I drove. …”

   NHTSA complaint #10147128, filed 2006-01, 113,000 miles

   “At various speeds, and under different braking conditions, the brakes fail. The failure is associated with a loud grinding noise. The failure is not the ABS because the noise is different.”

   NHTSA complaint #712326, filed 1999-09

Buying note. Have a pre-purchase inspection focus on the plastic upper intake manifold, coolant level and fuel system, since those account for most of what owners report on this model year. Ask for records showing whether the fuel pressure regulator recall was completed and whether the intake manifold has already been replaced.

Summary written with AI from a sample of 60 NHTSA complaints for this model year (picked at random, with complaints that state a mileage and recent ones taken first), then checked automatically against the source records. Where a problem shows a complaint count, every complaint for this model year was matched with fixed keyword rules (written with AI and tested against the sample), and the mileage, age and repair figures are calculated from those complaints; owners' figures are as stated, not verified. Other counts refer to the sample. The excerpts come from NHTSA's public complaint records and are unverified; capitalisation is normalised, NHTSA staff notes are removed, and shortened text ends with “…”. Something wrong? Request a correction.