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1999 Hummer Model Year Changes.

1999 saw some significant changes for the Hummer. Government regulations required the Hummer (which is a class III Truck) to have ABS for the first time. Unfortunately the Torsen differentials and the Brake/Throttle Modulation (BTM) Technique that made them so effective off-road were not compatible with the required Anti-lock Braking System. The solution to keeping the Hummer's Off-road prowess and complying with the regulations was Torque Trac 4 or TT4. This electronic system preforms a version of BTM but without driver participation. When wheel spin is detected, brake is automatically applied to the spinning wheel and torque is transferred to the wheel with traction. The new Torsen II differential works much the same as the old Torsen but with less torque bias. Manual BTM still works on the '99 Hummers but is not as effective because of the lower torque bias. Some owners love the TT4 system while others prefer the old system of manual BTM .

Powertrain and Identification Information.

  • VIN 10th Digit designating year = "X"
  • Engine: 6.5L Turbo Diesel 195 H.P. 430 lb. ft. VIN 4th digit ="Z"
  • 4L80E Electronic 4 speed Automatic Transmission. VIN 5th digit ="A"
  • Top Speed 83+ mph.
  • 831 '99 models built.
Significant changes for 1999.
  • 6.5L Turbo Diesel Standard. 6.5L NA Diesel no longer available.
  • First Year for Anti-lock Braking System (ABS)
  • First Year for TT4 Traction control system. TT4/ABS Video Click Here.
  • New Wiring Harness.
  • New fuse relay center.
  • CTI pump moved to new location.
  • Accessory fuse panel added.
  • New Power Steering Pump & reservoir.
  • New Power Steering Cooler.
  • New Water Pump.
  • Torsen II differentials.
  • New halfshafts with tone ring for detection of individual wheel speed.
  • New 4 Button remote entry.
  • New heated windshield glass.
  • New larger winshield washer reservoir.
  • New Color Night Storm.
  • New Color Mesa Dusk.
  • Green Metallic discontinued.
Valuable upgrades to look for in a '99.
  • Although steering components were upgraded several times by '99, the factory "Problem Solver" Idler and Pitman arms introduced in later years are much more durable than those on a '99.
  • Enhanced engine block- Turbo Diesel Engines with block castings before May 1999 are susceptible to #8 cylinder cracks. Most frequently the first symptom of a cylinder crack is coolant being forced out of the cooling system causing the "check coolant" light to illuminate. Many engines have been replaced with blocks of the same design. Even though the enhanced blocks were first produced in May 1999 it took some time before they made their way through the system and into Hummers as either original equipment or for replacement. Even Hummers produced in 2000 are likely to have the pre-May 1999 block casting. There is a casting number on the right rear of the block under the cylinder head which should be E_99 (May 1999) or later. Unfortunately the codes changed through the years so identifying the enhanced blocks is even more difficult. Later blocks also use metric bolts to attach the bell housing but it is unclear whether this clearly identifies an enhanced block. Although enhanced blocks were installed in Hummers produced before the engine manufacturer change to General Engine Products (GEP), the easiest way to make sure a Hummer left the factory with an enhanced block is to check the 4th digit of the VIN on 2001 and later 6.5L turbo diesels. If the 4th digit is an "F" the engine was produced by GEP and is sure to have the enhanced block from the factory.

'99 Specifications, options & Prices:
Available colors:
Mesa Dusk (C22). New Color for '99. Night Storm (B21). New Color for '99
Competition Yellow (Y20).
Candy Apple Red (R19).
Silver Metallic. (S15) White. (W8)
Black. (B9) Bright White. (W14)
Although most factory custom colors show up on emergency vehicles and as factory tests, custom colors were available on all Hummers for an additional $1,000 charge. Below is an example of a Hummer with a factory experimental color (X), Cactus Green. Cactus Green never made it into full production.
Body Styles Available in '99:
HMC4. 4-Passenger Hard Top. VIN 6th & 7th Digits "83"
HMCS. 4-Passenger Wagon. VIN 6th & 7th Digits "84"
XLC2. 2-Passenger Hard Top Enlarged Cab. VIN 6th & 7th Digits "89"
HMCO. 4-Passenger Full Door Open Top. VIN 6th & 7th Digits "90"
TOTAL PRODUCTION COUNT BY MODEL AND COLOR. "X" Colors are "Experimental" or special order, often seen as production colors in later years.
COLOR
FULL DOOR OPEN TOP (HMCO)
WAGON (HMCS)
HARD TOP (HMC4)
2-PASS. ENLARGED CAB (XLC2)
TOTAL
B21 (Nightstorm)
11
27
7
1
46
B9 (Gloss Black)
69
147
44
3
263
C22 (Mesa Dusk)
38
65
15
1
119
R19 (Candy Apple Red)
34
50
14
3
101
S15 (Silver)
12
33
12
1
58
W14 (Bright White)
28
58
15
15
116
W8 (Gloss White)
9
7
2
1
19
Y20 (Competition Yellow)
49
27
11
87
X02 (Safety Green)
1
1
X20 (Gloss Red R7)
5
5
X28 (Green )
1
2
3
X29 (Gloss Green (G10) )
1
2
3
X30 (Blue)
6
6
X31 ( Firetruck Red)
1
1
X32 (Green)
1
1
X33 (Pewter)
1
1
Tan Interior
114
165
35
314
Gray Interior
138
261
85
33
517
Cloth
220
401
108
20
749
Vinyl
32
25
12
13
82
TOTAL
252
426
120
33
831
© Copyright 2004 Jim Lynch.