This service bulletin provides information on some vehicles that may rock or move slightly forward or rearward while in Park at start up after cold soak. This condition may be accompanied by a clunk noise. This is a slight movement that is more often seen visually, rather than felt, when viewed from the outside and using the auto-start feature, if equipped.
full bulletin at NHTSA ↗2008 Chevrolet Impala powertrain problems
severe 80 complaints filed with NHTSA · avg repair $2,500 · see powertrain across all vehicles →
Failure mileage
Complaints
80
Recalls
0
Avg fix
$2,500
5crashes
6injuries
What stands out
Owners have filed 80 powertrain complaints with NHTSA against this vehicle, but no formal recall covers the issue — the federal record reflects what manufacturers have admitted, not everything owners are reporting.
Among the 15 model years of Chevrolet Impala in our records for powertrain problems, this one ranks #2 by owner-complaint volume.
Is there a fix? Manufacturer service bulletins
The manufacturer has issued service bulletins covering powertrain on this vehicle — documented repair instructions, service campaigns, or warranty extensions sent to dealers. A TSB isn't a recall (it's not a free safety remedy), but it's the manufacturer acknowledging the issue and how to fix it.
GM is receiving damaged (cracked or broken) transmission cores returned to the reman facilities. The damage is being caused either in the removal process by the technician, or inadequate packaging or shipping. This bulletin advises the dealers to be more careful not to damage the transmissions during removal and to package the core properly for return.
full bulletin at NHTSA ↗This bulletin provides information on the harmful effects of water or ethylene glycol in transmission fluid.
full bulletin at NHTSA ↗This service bulletin provides technicians with information to help identify the differences between what is considered a fluid leak, and what is considered fluid seepage.
full bulletin at NHTSA ↗This Warranty Admin service bulletin provides guidelines for Dealers Not Required and for Dealers Required to Contact the PQC for engine or transmission assembly replacement and explains the PQC process, GWM Transaction submission, vehicle service record retention and proper handling of assembly returns for Canadian Dealers only.
full bulletin at NHTSA ↗Source: NHTSA manufacturer communications. Bring the bulletin number to your dealer or shop.
The failure pattern owners describe
The 2008 Impala powertrain problems cluster around five distinct failure modes. Most common: the "engine power reduced" warning that limits the car to 40 mph or causes complete stall, often mid-drive. Owners describe multiple diagnostic visits and part replacements (throttle sensors, throttle pedal assembly, gas pressure sensor, temperature sensor, thermostat)—costing $900 to $1,300—with the warning returning days or weeks later.
Second: the shift lever locks in park, leaving owners stranded. Root cause is a broken wire in the shift lock control harness; some owners resort to manually pressing a release button under the console. Repair runs $91 to $465.
Third: transmission slip on takeoff. The car hesitates, revs without engaging, then jerks hard into gear. One owner reported a T-bone collision when the car lurched into another vehicle; another had a rear-end crash when the vehicle unexpectedly shifted into neutral at 70 mph.
Fourth: vehicle jerks violently when shifting, especially during acceleration from a stop—hazardous in traffic or with children aboard.
Fifth: accelerator pedal sensor code P2138 recurs repeatedly even after pedal replacement.
Dealers frequently cannot reproduce intermittent faults. GM has issued no recalls despite owners citing hundreds of identical complaints online.
Same Chevrolet Impala powertrain reports on nearby years: 2006 · 2007 · 2009 · 2010 · 2011
Failure modes owners describe
Reduced Engine Power / Throttle Control Failure
Engine power reduces to 40 MPH or vehicle stalls completely. Warning messages display "Engine Power Reduced," "Service Traction Control," "Starting Disabled," or "Service Throttle." Multiple owners report the message appears randomly, sometimes returns after repairs. Dealers struggle to diagnose; error codes may be generic or point to throttle/sensor issues.
When: Varies; some report within first 3 months of ownership, others at 80k+ miles. One owner reported recurring issue over 1+ year.
Symptoms owners cite: Engine loses power; vehicle limited to 40 MPH or less; Check engine light and service traction control lights illuminate; Vehicle stalls mid-drive with no warning; Hard downshift followed by stall; Car jerks or hesitates upon acceleration after the condition clears; Loss of power steering and power brakes when engine stalls; Message reappears after dealer diagnostics and repairs
Codes mentioned: P2138 (Accelerator Pedal Position Sensors 1-2 not plausible), P0172, Code 2127, Generic computer error codes
Repairs/costs cited: Owners report replacing: throttle pedal assembly, gas pressure sensor, APP sensor, temperature sensor, thermostat, pinched wire repairs, computer resets. Costs cited: $900–$1,300+. Many repairs do not permanently resolve the issue.
Recalls/TSBs owners mention: GM advised one owner that gas throttle sensor could be the cause, but offered no warranty coverage for diagnostics if sensor was not faulty. Some owners report GM paid for dealer diagnostics on second visit. No recalls issued for this problem despite multiple complaints.
Gear Shift Stuck in Park / Shift Lock Failure
Shift lever locks in park position and will not disengage. Owners must restart vehicle multiple times, use manual release button under console, or have wires reconnected by mechanic. Root cause identified as broken or disconnected wiring in the shift lock control harness.
When: Occurs intermittently. Some owners report after parking on incline; others report random occurrence while parked.
Symptoms owners cite: Shift lever completely locked; will not move from park; Vehicle stranded and unable to move; Requires repeated engine restart attempts to release shift; Manual release button under console used as temporary workaround; On one vehicle, keys stuck in ignition switch
Codes mentioned: Shift lock control solenoid inoperative
Repairs/costs cited: Road service and mechanics found: broken wire in shift lock control harness (black wire), melted green wire ~12 inches from shifter, high-resistance connector. Repair costs cited: $91–$465. One owner reports having to use screwdriver to manually push release button under console. Mechanic noted wire too short by design, causing tangling and breakage.
Recalls/TSBs owners mention: One owner reported GM advised them no recall exists and warranty does not cover issue (beyond 36k miles bumper-to-bumper). Mechanic noted "not uncommon" and that GM appears aware of the issue based on repair order wording. No factory recalls issued.
Transmission Slip / Harsh Jerking on Acceleration
Transmission slips or hesitates when taking off from stop. Vehicle lurches, jerks hard, or revs engine without engaging. Occurs at traffic lights, highway merges, and low-speed starts. One collision reported when car lurched into another vehicle.
When: Some owners report from early ownership; others at 30k–85k miles. Intermittent, worsening over time.
Symptoms owners cite: Transmission does not engage when stepping on gas; Engine revs with no acceleration; transmission slips; Hard jerk when transmission finally catches; Hesitation followed by sudden acceleration; Lurching motion throws occupants (child mentioned); Transmission jerks with every gear shift; Repeat failures after dealer service; Works fine if shifted manually
Repairs/costs cited: Owners report replaced: fuel pump, spark plugs, coil, fuel injector (twice), transmission control solenoid, throttle pedal assembly. One owner needed full transmission replacement at 55k miles; replacement transmission began exhibiting same torque converter shudder. Costs not fully detailed but described as "quite costly."
Recalls/TSBs owners mention: Dealers unable to diagnose intermittent failure without reproducing it. One owner reports GM refuses to acknowledge flaw in 4T65-HD transmission. No recalls issued despite owner research showing pattern across multiple forums.
Transmission Shift into Neutral / Unintended Downshift
Vehicle erroneously shifts into neutral or low gear while driving, causing engine to stall or vehicle to lose power. Two owners report collision incidents when vehicle shifted unexpectedly.
When: One report at 65 MPH on highway; another at 70 MPH; another at decelerating to stop or accelerating from stop.
Symptoms owners cite: Vehicle shifts into neutral unexpectedly while driving; Engine stalls when shift into neutral occurs; Vehicle loses power and cannot recover; Shift to low gear with violent jerking while decelerating or accelerating from stop; Loss of control leading to rear-end collision
Codes mentioned: Fractured gear shift wiring
Repairs/costs cited: Mechanic/dealer diagnosed fractured gear shift wiring requiring replacement. One accident report noted no repairs made due to vehicle not taken for service after crash.
Recalls/TSBs owners mention: Manufacturer was notified in at least one case. No recall issued.
Accelerator Pedal / Sensor Malfunction
Accelerator pedal sensor fails, causing erratic engine behavior, reduced power, or stalling. Code P2138 indicates pedal position sensor discord. Owner replaced pedal twice; code returns.
When: Started 3 months after ownership; recurs every 3–4 days after clearing code.
Symptoms owners cite: Check engine light flashing; Reduced engine power message; Engine warning light on/off every 3–4 days even after code clearing
Codes mentioned: P2138 (Accelerator Pedal Position Sensors 1-2 not plausible), P0172
Repairs/costs cited: Owner reports father replaced accelerator pedal twice and erased code both times; code returns. AutoZone confirmed same codes. No permanent fix achieved.
Recalls/TSBs owners mention: Chevrolet dealership representative stated no recall exists for vehicle.
Synthesized from 80 NHTSA owner complaints — unverified consumer allegations, summarized for patterns. The verbatim filings appear below.
What owners are reporting 0 most recent
Had powertrain trouble with your 2008 Chevrolet Impala?
File a complaint with NHTSA → It's free, official, and how every report above got here — owner filings are the federal safety record this page is built on.
Common questions
How serious is the powertrain problem on the 2008 Chevrolet Impala?
It's a meaningful issue. 80 complaints have been filed and the failure mode causes operational problems for owners. Repairs average $2,500.
At what mileage does the powertrain typically fail?
Across the 66 complaints that reported odometer mileage, most powertrain failures cluster between 65,000 and 109,890 miles, with the median around 81,352. A quarter of owners report trouble before 65,000; a quarter make it past 109,890. Maintenance history matters more than the odometer alone — this is the reported failure window, not a guarantee.
What does it cost to fix?
Independent shops typically charge around $2,500 for powertrain repairs on this vehicle. Dealer pricing tends to run 20-40% higher. The exact figure depends on the specific failure mode, parts availability, and your local labor rates. If you're outside factory warranty, an extended service contract often covers this category.
Are there any recalls related to powertrain?
No active recalls currently cover powertrain issues on this vehicle. The complaints filed represent owner-reported failures that haven't risen to the level of a manufacturer-issued recall — but they're still worth knowing about before you buy or budget for repairs.
Related
Complaint and recall data sourced from the National Highway Traffic Safety Administration (NHTSA)
public records database. Verify the raw federal record at
nhtsa.gov/vehicle/2008/Chevrolet/Impala.
Severity ratings are derived from reported crashes, fires, injuries, and fatalities. Repair cost estimates are
independent-shop national averages and may differ in your area. Some links on this page are affiliate links.