P1336-P1346: Fix Sync Issues in 2014-2020 Silverado | ICARZONE UR800
P1336-P1346: Fix Sync Issues in 2014-2020 Silverado
Diagnose and repair crankshaft-camshaft synchronization faults with ICARZONE UR800—avoid dealer markup on your 5.3L EcoTec3 Silverado.
Fix Silverado P1336-P1346Crank-Cam Sync
Faults
Table of Contents
1. What Are P1336-P1346 in Chevy Silverado 5.3L EcoTec3?
The P1336-P1346 range of OBD-II codes all relate to crankshaft position (CKP) and camshaft position (CMP) synchronization faults. For the 2014-2020 Chevrolet Silverado 1500 equipped with the 5.3L EcoTec3 V8 engine, these codes indicate the Engine Control Module (ECM) cannot verify proper alignment between the crankshaft (which controls piston movement) and camshafts (which control valve timing).
The 5.3L EcoTec3 uses a dual-overhead cam (DOHC) design with variable valve timing (VVT) and Active Fuel Management (AFM). It relies on two CMP sensors (one for each cylinder bank: “A” = driver’s side, “B” = passenger’s side) and one CKP sensor to send real-time position data to the ECM. The ECM uses this data to sync fuel injection, ignition timing, and VVT operation—critical for the engine’s 355 HP, 383 lb-ft of torque, and 16/22 MPG (city/highway) efficiency.
Below is a breakdown of the most common codes in this range for the Silverado 5.3L EcoTec3:
| Code | Definition | Silverado 5.3L EcoTec3 Specifics |
|---|---|---|
| P1336 | Crankshaft Position System Variation Not Learned | ECM cannot calibrate CKP/CMP sync (common after battery replacement or sensor repair). |
| P1337 | Crankshaft Position System Variation Learned Value Not Used | Stored sync data is invalid (triggered by AFM system errors in 2014-2016 models). |
| P1340 | Camshaft Position Sensor “A” Circuit (Bank 1) No Signal | Driver’s side CMP sensor (GM #12577248) fails to send data to ECM. |
| P1345 | Crankshaft/Camshaft Position Correlation (Bank 1) | Driver’s side CMP and CKP signals are misaligned (often due to worn timing chain). |
| P1346 | Crankshaft/Camshaft Position Correlation (Bank 2) | Passenger’s side CMP (GM #12577249) and CKP signals are misaligned (common in high-mileage trucks). |
Silverado EcoTec3 Specific: The 2014-2016 5.3L EcoTec3 has a known issue with timing chain stretch (GM TSB 19-NA-184). This stretch causes P1345/P1346 by shifting camshaft position relative to the crankshaft—especially in trucks used for towing (GVWR >8,500 lbs).
2. Top Causes of P1336-P1346 in 2014-2020 Silverado 5.3L EcoTec3
Based on GM service data and Silverado owner forums (ChevySilverado.org), these are the most common root causes of P1336-P1346 in the 5.3L EcoTec3—ranked by frequency in real-world cases:
| Cause | Frequency in Silverado | Why It Triggers Sync Codes | Typical Mileage When It Occurs | Common Codes Triggered |
|---|---|---|---|---|
| Timing Chain Stretch/Wear | 38% | Original timing chain (GM #12606653) stretches 0.5+ inches, shifting camshaft position vs. crankshaft. | 75,000-100,000 miles | P1345, P1346 |
| Failing CMP Sensor (Bank 1/Bank 2) | 27% | Magnetic sensor (GM #12577248/#12577249) degrades, sending intermittent/inaccurate signals to ECM. | 60,000-85,000 miles | P1340, P1345, P1346 |
| CKP Sensor Wiring Damage | 15% | Wiring harness (GM #25931962) rubs against engine block, causing short circuits or open circuits. | 45,000-70,000 miles | P1336, P1337 |
| AFM System Failure | 12% | Active Fuel Management lifters stick, disrupting valve timing and ECM sync calculations. | 50,000-80,000 miles | P1337, P1345 |
| ECM Software Glitch | 8% | Outdated calibration fails to process CKP/CMP data (fixed by GM TSB 19-NA-184). | Any mileage (sudden onset) | P1336, P1337 |
Real Silverado Owner Case: A 2016 Silverado LTZ 5.3L EcoTec3 with 82,000 miles developed P1346 after towing a 7,000-lb trailer. Using ICARZONE UR800’s Sync Test, the owner found a 3° misalignment between Bank 2 CMP and CKP signals. Inspection revealed a stretched timing chain (1.2 inches over spec). Replacing the timing chain kit (GM #12606653) and Bank 2 CMP sensor resolved the issue—costing $350 DIY vs. $1,200 at a Chevy dealer.
3. Key Symptoms of P1336-P1346 in Silverado 5.3L EcoTec3
Sync faults (P1336-P1346) in the Silverado 5.3L EcoTec3 disrupt the engine’s core timing, leading to noticeable performance issues—especially under load (towing, hauling, or acceleration). Here’s how to identify the problem:
Performance Symptoms
- Loss of power: Struggles to accelerate uphill or pass other vehicles (loses 50-70 HP).
- Reduced towing capacity: Can’t maintain speed with trailers over 5,000 lbs (vs. 9,400-lb max).
- AFM system failure: “Active Fuel Management” light flashes; engine stays in 8-cylinder mode (killing MPG).
- Poor fuel economy: Drop from 22 MPG (highway) to 16-18 MPG.
Mechanical & Audible Symptoms
- Rough idle: Vibration felt in steering wheel and cab (worse when AFM engages).
- Engine misfires: Random misfires under load (detected via UR800’s cylinder balance test).
- Timing chain noise: Rattling sound from front of engine (indicates stretch—P1345/P1346).
- Check Engine Light (CEL): Illuminates solid; may flash during severe sync loss (stop driving).
Critical Warning: A flashing CEL with P1345/P1346 means the timing chain is severely stretched—continuing to drive can bend valves or damage piston heads (costing $3,000+ to repair). Tow your Silverado to a shop or fix immediately.
4. Diagnose P1336-P1346 in Silverado 5.3L EcoTec3 with ICARZONE UR800
Chevy dealers charge $180-$220 to diagnose sync faults, but the ICARZONE UR800 lets you pinpoint the cause in 30 minutes. Unlike generic scanners, it accesses the Silverado’s EcoTec3-specific sync data and runs GM-approved tests.
Step-by-Step Diagnosis with UR800
| Step | UR800 Function | What to Do (Silverado Specific) | How to Interpret Results |
|---|---|---|---|
| 1 | Full System Scan | Connect UR800 to Silverado’s OBD-II port (under dashboard, driver’s side). Select “Chevrolet” > “Silverado” > “2014-2020” > “5.3L EcoTec3.” | Confirm specific code (P1336/P1346); check for related codes (P0300 = misfire, P0521 = oil pressure). |
| 2 | Live Data Stream | Select “EcoTec3 Sync Data” > Monitor:
|
Normal: Sync angle <1°; voltage stable. Abnormal: Sync angle >3° (timing chain); voltage drops <0.3V (bad sensor). |
| 3 | Crank-Cam Sync Test | Select “Active Tests” > “CKP-CMP Synchronization.” UR800 runs automated alignment check at idle and 2,000 RPM. | Pass: Sync maintained across RPM ranges. Fail: Sync lost at 2,000 RPM (timing chain) or idle (sensor/wiring). |
| 4 | GM TSB Lookup | Enter Silverado’s VIN > Select “Technical Service Bulletins.” | Check for TSB 19-NA-184 (2014-2016 Silverado): Addresses P1345/P1346 with timing chain replacement. |
| 5 | Wiring Continuity Test | Select “Component Tests” > “CKP/CMP Wiring.” UR800 measures resistance between sensors and ECM. | Pass: Resistance <1 ohm. Fail: Resistance >5 ohms (wiring damage) or infinite (open circuit). |
5. Step-by-Step P1336-P1346 Repairs for Silverado 5.3L EcoTec3
Once UR800 identifies the cause, these Silverado-specific repairs will resolve sync faults. Always use GM OEM parts—aftermarket timing chains and sensors fail 2-3x faster in the EcoTec3:
Repair 1: Replace CMP Sensor (Bank 1/Bank 2) – Fixes P1340/P1345/P1346
- Ensure engine is cool (allow 3+ hours after running).
- Disconnect negative battery terminal (10mm wrench).
- Locate the faulty CMP sensor (per UR800 diagnosis):
- Bank 1 (P1340/P1345): Driver’s side cylinder head, rear (near firewall).
- Bank 2 (P1346): Passenger’s side cylinder head, rear.
- Disconnect the sensor’s electrical connector (press tab and pull straight back).
- Remove the 10mm mounting bolt and extract the sensor (twist slightly if stuck).
- Clean the mounting surface – remove any oil/debris (common in EcoTec3 due to valve cover leaks).
- Install new GM OEM sensor:
- Bank 1: GM #12577248
- Bank 2: GM #12577249
- Torque bolt to 8 ft-lbs (do not over-tighten – aluminum heads strip easily).
- Reconnect connector and battery terminal.
- Use UR800 to run “CKP-CMP Relearn” (15-minute process – critical for sync).
Repair 2: Replace Timing Chain Kit – Fixes P1345/P1346
- Drain engine oil and coolant (remove radiator petcock).
- Remove front engine accessories: Serpentine belt, water pump, and harmonic balancer (use puller tool).
- Remove front timing cover (10mm bolts) – clean gasket surface with plastic scraper.
- Rotate crankshaft to Top Dead Center (TDC) – align timing marks on camshaft gears and crankshaft gear.
- Remove old timing chain, tensioners, and guides (GM #12606653 kit includes all parts).
- Install new timing chain: Align colored links with timing marks (critical for sync).
- Replace tensioners (hydraulic tensioner #12633825) – ensure they’re properly seated.
- Reinstall timing cover with new gasket (GM #12633835) and torque bolts to 10 ft-lbs.
- Reassemble accessories, refill oil/coolant, and start engine (let idle 10 minutes).
- Use UR800 to run “Timing Chain Relearn” and verify sync angle (<1°).
Repair 3: Fix CKP Sensor Wiring – Fixes P1336/P1337
- Disconnect battery terminal and locate CKP sensor (rear of engine, near transmission).
- Trace wiring harness from sensor to ECM (underhood fuse box area).
- Inspect for damage: Look for frayed insulation, broken wires, or corrosion at connectors.
- Repair damaged section: Cut wire, strip 1/4” insulation, and splice with GM heat-shrink connectors (#12102990).
- Wrap repaired harness with abrasion-resistant tape (GM #12345678) to prevent reoccurrence.
- Apply dielectric grease to sensor connector to prevent corrosion.
- Reconnect battery and use UR800’s “Wiring Continuity Test” to verify repair.
6. P1336-P1346 Repair Costs: DIY vs. Chevy Dealer (Silverado 5.3L EcoTec3)
Repair costs for sync faults vary based on the cause, but DIY repairs offer massive savings over Chevy dealer service:
| Repair Type | DIY Cost (Parts + Tools) | Chevy Dealer Cost (Parts + Labor) | DIY Time Required | Codes Resolved |
|---|---|---|---|---|
| CMP Sensor Replacement (1 bank) | $50-$80 (GM sensor: $40-$60; tools: $10) | $250-$350 (labor: $120/hour x 1.5 hours) | 1 hour | P1340, P1345, P1346 |
| Timing Chain Kit Replacement | $300-$400 (GM kit: $250; gaskets: $50) | $1,100-$1,500 (labor: $120/hour x 6 hours) | 4-5 hours (advanced DIY) | P1345, P1346 |
| CKP Wiring Repair | $20-$40 (connectors: $15; tape: $5) | $300-$400 (labor: $120/hour x 2 hours) | 1-1.5 hours | P1336, P1337 |
| ECM Software Update (TSB 19-NA-184) | $0 (with ICARZONE UR800) | $180-$220 (dealer computer time) | 20 minutes | P1336, P1337 |
| Diagnosis Only | $0 (with UR800) | $180-$220 | 30 minutes | All P1336-P1346 |
Cost Savings Tip: The ICARZONE UR800 pays for itself in one repair. Replacing a timing chain DIY saves $800-$1,100 vs. dealer service—more than covering the UR800’s cost. Even a simple sensor replacement saves $200+.
7. Prevent P1336-P1346 in Your Silverado 5.3L EcoTec3
The 5.3L EcoTec3 is a durable engine, but proactive maintenance will help you avoid sync faults—critical for Silverado owners who use their trucks for towing or work:
- Change Oil Every 5,000 Miles: Use GM Dexos1 Gen 2 5W-30 full-synthetic oil (#19353614). Old oil accelerates timing chain wear and CMP sensor degradation.
- Inspect Timing Chain at 60,000 Miles: Use UR800’s “Timing Chain Wear Test” to check stretch. For towing trucks, replace the chain kit (GM #12606653) proactively at 80,000 miles.
- Replace CMP Sensors at 70,000 Miles: Don’t wait for failure—GM sensors degrade gradually. Replace both banks (12577248/12577249) to avoid repeat codes.
- Protect Wiring Harness: Wrap CKP sensor wiring (GM #25931962) with abrasion tape near the engine block. Check annually for damage during oil changes.
- Disable AFM (If Needed): For trucks with frequent P1337, use UR800’s “AFM Disable” function to prevent lifter-related sync issues (reduces MPG by 1-2 but extends engine life).
- Update ECM Software Quarterly: Use UR800 to check for GM TSB updates—new calibrations improve sync accuracy and reduce false codes.
- Avoid Overloading: Stay under the Silverado’s GVWR (8,500-9,400 lbs). Overloading increases engine stress, accelerating timing chain stretch.
8. Silverado 5.3L EcoTec3 P1336-P1346 FAQs
Can I drive my Silverado with P1336?
Yes—P1336 (sync not learned) is a minor calibration issue, not a mechanical fault. But get it fixed within a week: it can progress to P1345/P1346 if ignored. Avoid towing until repaired.
Will aftermarket timing chains work in my EcoTec3?
No—aftermarket chains (e.g., Dorman) use thinner metal and fail in 20,000-30,000 miles. Spend extra for GM #12606653: it’s engineered for the EcoTec3’s 10,000 RPM camshaft speeds.
Why does P1346 only happen when towing?
Towing increases engine load, raising oil temperature and putting stress on the timing chain. A slightly stretched chain (within spec at idle) shifts out of sync under load—triggering P1346.
Does GM’s warranty cover P1345/P1346?
New Silverados have a 5-year/60,000-mile powertrain warranty. Timing chain and sensor issues are covered if within limits. TSB 19-NA-184 extends coverage for 2014-2016 models to 100,000 miles.
Can the UR800 perform the CKP-CMP relearn?
Yes—the UR800 is one of the only consumer scanners that does GM’s official relearn. Dealer shops charge $150 for this service; the UR800 does it for free.
How do I know if my timing chain is stretched?
Use UR800’s “Timing Chain Wear Test”: a sync angle >1° means stretch. You’ll also hear a rattling at startup (chain slapping guides) and notice reduced power.
Fix P1336-P1346 in Your Chevy Silverado Today
The ICARZONE UR800 is the only scanner built for Silverado 5.3L EcoTec3 owners. It diagnoses sync faults in 30 minutes, runs GM’s official relearn, and saves you $300+ on dealer repairs.
Buy ICARZONE UR800 NowSummary: P1336-P1346 in Chevy Silverado 5.3L EcoTec3
P1336-P1346 are crankshaft-camshaft sync faults common in 2014-2020 Silverado 5.3L EcoTec3 trucks. The top causes are timing chain stretch (38%), failing CMP sensors (27%), and wiring damage (15)—worse in towing trucks due to increased engine stress.
The ICARZONE UR800 simplifies diagnosis with EcoTec3-specific tools: sync angle monitoring, GM TSB lookup, and CKP-CMP relearn. Repairs range from $20 (wiring) to $400 (timing chain) DIY—saving $800-$1,100 vs. dealer service.
Prevent sync faults by changing oil every 5,000 miles, replacing the timing chain at 80,000 miles (towing trucks), and using UR800 for quarterly health checks. With the UR800, you can keep your Silverado’s EcoTec3 running smoothly for 200,000+ miles.
