Supplement to 03-06-01-024B 4.3L LU3 L35 Timing Chain Tensioner - kw balance chain cover gasket noise pump rattle shaft warranty

The following diagnosis might be helpful if the vehicle exhibits the symptom described in the PI.

Rattle-type noise coming from the engine at approximately 1800 to 2200 RPMs - The spark, rattle-type noise may be caused by torsional vibration of the balance shaft. The 2003 and 2004 4.3 L LU3 Vin code X engines will not accept the service timing chain tensioner fix as per bulletin 03-06-01-024B. Prior to June 2003 all 4.3 LU3 engines will accept the service timing chain tensioner as per bulletin 03-06-01-024B. This PI is a supplement to Bulletin 03-06-01-024B and applies only to engines built between June 2003 and September 2003.

The production timing chain tensioner was put into all engines beginning with the Julian date of 251 (September 8, 2003); the engines on or after this date code should not have customer concerns of balance shaft rattle. (The engine unit number and Julian date code locations are explained below.)

Complete the proper SI diagnostic for engine noise. If detonation noise is present, perform detonation/spark knock diagnostics first. If the Balance shaft rattle noise has been verified on a 2003 or 2004 4.3L LU3 engine the dealer will need to check the engine Julian date. The engine Julian date can be found on the Engine Unit Number bar code label. The Engine Unit Number label can be found on the right side of the oil pan, left rear of the cylinder head, or the right front of the valve cover. This label has a fifteen character number on it. The 9th, 10th, and 11th digit of this 15 character number is the Julian date. The Julian dates are listed below with their proper service fixes.

JULIAN DATE 153 (JUNE 2, 2003) TO JULIAN DATE 200 (JULY 19, 2003)

1. If the engine is between the Julian dates of 153 to 200 and the customer concern of balance shaft rattle has been verified, there is no service fix and the engine will need to be replaced.

JULIAN DATE 202 (JULY 21, 2003) TO JULIAN DATE 227 (AUGUST 15, 2003)

1. Between the Julian dates of 202 and 227 there are mixed configuration blocks. The configuration of the block can be identified by an orange or purple dot found on at the rear of the block near the balance shaft boss and next to the knock sensor.

A. If the block has an orange dot, the block has non-machined timing chain tensioner bosses and will not accept the service fix or a production timing chain tensioner. If the customer concern of balance shaft rattle has been verified the engine will need to be replaced.

B. If the block has a purple dot, the block is fully machined and it will accept the production timing chain tensioner. The dealer will need to use the 2004 Model Year LU3 replacement parts for the Timing Chain Tensioner Bracket, Timing Chain Tensioner Bolt, and the Timing Chain Tensioner Shoe to install the production timing chain tensioner. The parts from bulletin 03-06-01-024B will not fit.

JULIAN DATE 230 (AUGUST 18, 2003) TO JULIAN DATE 251 (SEPTEMBER 8, 2003)

1. If the engine is between the Julian dates of 230 and 251 the block is fully machined and it will accept the production timing chain tensioner. The dealer will need to use the 2004 Model Year LU3 replacement parts for the Timing Chain Tensioner Bracket, Timing Chain Tensioner Bolt, and the Timing Chain Tensioner Shoe to install the production timing chain tensioner. The parts from bulletin 03-06-01-024B will not fit.

Alternative Method Of Identification:

Remove the front cover and inspect the front of the block.

1. If the timing chain tensioner bosses are present and are not machined, the surfaces of the bosses will be rough in appearance with no holes drilled. Neither the service kit or production kit will fit. Replace the engine.
2. If the timing chain tensioner bosses are present and machined, the surfaces will have a flat machined surface with holes drilled, the upper hole threaded for a bolt, the lower hole is machined smooth for a locator pin, see SI information for Timing Chain, Sprockets, and/or Tensioner Replacement for proper identification. Install the production timing chain tensioner for the 04 model year.
3. If there are no bosses cast into the block the service kit should be installed as per bulletin 03-06-01-024.

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Please follow this diagnosis process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed. If these steps do not resolve the condition, please contact GM TAC for further diagnostic assistance.

(03 04 C1 C2 K1 K2 S1 S6 T1 T6 M1 Chevrolet Silverado Astro Express S-10 Blazer) and (03 04 C1 C2 K1 K2 S1 S6 T1 T6 M1 GMC Sierra Savana Safari Sonoma Jimmy)

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