Original GoTech overview and diagnostic outline, combined here. Match the exact vehicle and current service information before using a procedure.
Start with what the engine is doing
A rattle, rough idle or loss of power can send you looking at the timing system. Record when it happens and pull the stored codes. Those clues get the diagnosis started; they don’t prove the chain is bad.
No check-engine light? Don’t stop at the code scan. Our 2014 Impala case had a real, bank-specific misfire without a stored code.
Find the bank and camshaft in your codes
Here’s the relationship each code points to in the GM diagnostic outline. The label tells you where to look—not which part to order.
| DTC Code | Bank / camshaft indicated |
|---|---|
| P0008 | Bank 1 · engine-position relationship |
| P0009 | Bank 2 · engine-position relationship |
| P0016 | Bank 1 Intake |
| P0017 | Bank 1 Exhaust |
| P0018 | Bank 2 Intake |
| P0019 | Bank 2 Exhaust |
What if the codes point to only one bank?
Use that bank and camshaft to focus the VVT and timing checks. Each bank has its own secondary chain, but a one-bank pattern does not prove that chain is faulty.
What if both banks have correlation codes?
The primary chain affects both banks. Keep that relationship in view, along with related signal and VVT faults. The pattern tells you what to investigate; it does not select a replacement kit.
Before you call it a timing-chain job
Find the code above, then work through the related systems. A comparison only helps if you can trust the signals and the conditions.
Quick terms: VVT, engine code and correlation
- VVT
- Variable valve timing: the system changes camshaft timing. Its operation is part of the checks below.
- RPO / engine code
- The engine identifier used to match service information and parts. Displacement alone does not identify the version.
- Cam/crank correlation
- The relationship between the camshaft and crankshaft position signals.
1. Match the engine and service information
- Identify the exact vehicle and engine application.
- Check applicable service information and bulletins for the codes and symptoms. Resolve their prerequisites before moving down the list.
2. Deal with related sensor faults
- Review camshaft- and crankshaft-sensor faults: an unreliable signal can undermine the correlation check.
- Review VVT-related faults: a commanded or actual cam-position problem can change the relationship you are measuring.
- Diagnose those related faults using the vehicle’s procedure before treating a correlation code as proof of mechanical chain wear.
3. Check VVT operation
- Check the VVT system using the vehicle’s procedure, concentrating on the bank and camshaft named by the codes.
- Check whether solenoid or phaser operation is changing the timing relationship before blaming mechanical chain wear.
- Need the background? How variable valve timing works →
4. Verify the timing relationship
- A scope can compare the cam and crank signals. Use the correct engine reference and matching test conditions.
- Follow service information for mechanical verification and any access needed to inspect the timing components. A waveform offset alone does not name the failed part.
- Open the scope setup and reference images →
One primary chain. Two secondary chains.
Conceptual relationship only—not a chain-routing diagram. The code pattern narrows the question; it doesn’t identify a failed chain.
See the actual chain and bank illustration →Does the engine version or oil history change the check?
Yes. Match the vehicle, build and engine RPO before choosing parts, service information or a reference waveform. LY7, LLT and later 3.6L variants are not one interchangeable repair application.
The timing and VVT systems rely on lubrication. Include oil condition and service history in the investigation, but don’t use either as proof that a particular part failed.
Our replacement series uses an engine being prepared for a 2011 Traverse. The donor year and RPO were not confirmed.
What this looks like on a real car
The Impala had no codes, but cylinders 1, 3 and 5 were counting misfires. Bank 1 fuel trim was different from bank 2. That led to compression and vacuum checks, then a cam/crank comparison.
Each result changed the next question. The relative-compression result was inconclusive. The vacuum pattern supported a bank-specific concern. The timing comparison then showed a bank 1 discrepancy.
Follow the Impala diagnosis, test by test →The referring shop took the Impala back for repair; that outcome is not documented here.
What did the check establish?
Related sensor or VVT fault still unresolved
You don’t yet have a reliable basis for blaming the chain. Follow that fault’s service procedure, then reassess the correlation concern.
Scope setup or reference doesn’t match
Check signal identity, engine/application, operating conditions and the reference before comparing the patterns. Use the scope comparison checklist.
A timing discrepancy is supported
The next question is the mechanical cause. Verify it with the correct service procedure; the waveform alone does not name the part that failed.
The cause is still unexplained
For applicable vehicles with two or more listed codes, GM’s historical PIP3423P considers reluctor movement after service-information diagnosis and chain/tensioner checks have not found the cause.
Take these questions to the shop
Keep the findings, work and final checks in the same conversation.
Read the checklist
GOTECH · SHOP CHECKLIST
GM timing concern: shop checklist
Use with the exact vehicle and engine. A code or waveform offset does not identify the failed part. These are discussion questions, not a repair diagnosis.
- What is the engine doing?
Bring the symptoms, when they happen, all codes and the exact engine identification. No warning light does not rule out a real complaint.
- What related faults need checking?
Ask about sensor signals and VVT operation on the bank/cam named by the codes before assuming chain wear.
- What finding supports the proposed repair?
If a scope comparison is used, ask whether the engine/reference and test conditions match. How will the mechanical cause be established?
- What will verify the repair?
Agree on reassembly and the checks for the original complaint. Clearing a code alone does not establish that the cause is resolved.
Use this to agree on the next check. It does not replace your vehicle’s service information or a written estimate.
Guide: https://gotech.com/articles/gm-3-6l/gm-3.6l-timing-chain
Take the finding to the next step
After repair, return to the original complaint and the relevant verification procedure. Clearing a code alone does not show that the underlying cause is resolved.
Explore the GM timing guides
Source and limits
Original GoTech article, 2022-06-09. Illustrations retain their source descriptions; their technical meaning has not been independently reviewed. Videos and articles remain separate evidence.
Existing tool links may earn GoTech a commission. Commercial descriptions remain attributed to the original article.
Article provenance
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