1. What Are P1550-P1551 in BMW 3 Series E90?

P1550 and P1551 are BMW-specific diagnostic trouble codes related to the Throttle Actuator Control (TAC) System. In 2006-2013 BMW 3 Series E90 models—particularly the 328i (N52 engine) and 335i (N54/N55 engines)—these codes indicate critical faults in the electronic throttle control system that manages air intake and engine power.

Breaking down the codes:

• P1550: "Throttle Actuator Control System - Malfunction" — General failure in the TAC system communication or operation.
• P1551: "Throttle Actuator Control System - Electrical Fault" — Specific electrical issue (e.g., short, open circuit) in the throttle actuator circuit.

The E90’s electronic throttle system replaces traditional mechanical linkages with sensors and motors: the accelerator pedal position sensor (APPS) sends driver input to the DME (Digital Motor Electronics, BMW’s ECM), which then commands the throttle actuator (motor) to open/close the throttle plate. This system is critical for the 3 Series’ responsive performance (0-60 mph in 5.3-7.0 seconds) and 28 MPG highway efficiency.

2. Top Causes of P1550-P1551 in 2006-2013 BMW E90

Based on BMW service records and E90 owner forums (Bimmerpost.com), P1550-P1551 in 3 Series models stem from five primary issues—with distinct patterns in N52 (328i) vs. N54/N55 (335i) engines:

3. Key Symptoms of P1550-P1551 in BMW E90

P1550-P1551 in the 3 Series create distinct symptoms due to the E90’s drive-by-wire system, which directly impacts throttle response—a hallmark of BMW’s "Ultimate Driving Machine" reputation:

4. Diagnose P1550-P1551 in BMW E90 with ICARZONE UR800

BMW dealers charge $180-$220 to diagnose P1550-P1551, often requiring DME scans and throttle adaptation tests. The ICARZONE UR800 lets you pinpoint the cause in 10 minutes—with BMW-specific tools that generic scanners lack, like E90 throttle actuator activation and DME coding checks.

Step-by-Step Diagnosis with UR800

5. DIY Video Tutorial

You can check some tutorial videos on YouTube about how to diagnose and repair P1550-P1551 code step-by-step.

6. Detailed P1550-P1551 Repair Procedures for BMW E90

Once the UR800 identifies the cause of P1550-P1551, these E90-specific repairs will resolve the issue. For BMW components, use OEM or Bosch parts—aftermarket throttle actuators often fail BMW’s strict calibration requirements:

Repair 1: Replace Throttle Actuator (Most Common Fix)

1. Ensure engine is cool (2+ hours) and disconnect negative battery terminal (10mm wrench).
2. Remove engine cover: Lift straight up (328i) or remove 4 Torx screws (335i) to access intake manifold.
3. Remove air intake components:
   • Loosen hose clamps on air filter box and turbo inlet (335i) or MAF housing (328i).
   • Disconnect MAF sensor connector (press tab and pull).
   • Remove 2-4 bolts securing air intake tubes (10mm socket).
4. Locate throttle actuator: Mounted on the intake manifold, with a 6-pin electrical connector and 4 mounting bolts.
5. Disconnect electrical connector: Press tab and pull straight back. Note: Take photos of connector orientation for reinstallation.
6. Remove actuator mounting bolts: 4 bolts (8mm socket) secure the actuator to the intake manifold. Remove carefully to avoid dropping bolts into engine bay.
7. Clean mating surface: Use a plastic scraper to remove old gasket material from intake manifold. Wipe clean with lint-free cloth and isopropyl alcohol.
8. Install new actuator (BMW OEM #13547585229):
   • Install new gasket (included with actuator) onto intake manifold.
   • Position actuator and hand-tighten all 4 bolts before torquing to 8 ft-lbs (10.8 Nm) in crisscross pattern.
   • Reconnect electrical connector until it clicks into place.
9. Reinstall air intake components in reverse order of removal.
10. Reconnect battery and use UR800 to perform "Throttle Adaptation" (critical step):
    • Select "BMW" > "E90" > "Throttle Adaptation."
    • Follow on-screen prompts (engine off, key on for 30 seconds).
    • Clear P1550-P1551 codes and test drive.

Repair 2: Replace Damaged Wiring Harness (TSB Fix)

1. Complete steps 1-3 from actuator replacement (above) to access engine bay.
2. Locate the throttle actuator harness: Runs from actuator to DME (behind glove box in E90).
3. Disconnect harness at both ends:
   • Disconnect from throttle actuator (step 5 above).
   • Access DME: Open glove box, remove 2 Torx screws, pull DME cover down, disconnect harness (press tab).
4. Remove harness from clips: Use small screwdriver to release plastic clips securing harness to engine bay.
5. Install updated TSB harness (BMW #12517585923):
   • Route new harness through same path as old one, ensuring it’s clear of hot components.
   • Use new clips (included) to secure harness—pay extra attention to sections near air intake.
   • Reconnect to actuator and DME, ensuring proper clicks.
6. Replace air intake housing (if cracked): 328i N52 models use housing #13717547429—install new o-ring seals to prevent future water intrusion.
7. Reassemble components and use UR800 to run "Wiring Integrity Test" (should show 0.5-2.0 ohms resistance).

7. P1550-P1551 Repair Costs: DIY vs. BMW Dealer (E90)

Repair costs for P1550-P1551 in BMW E90 models vary based on the cause, but DIY repairs with the ICARZONE UR800 offer significant savings over BMW dealer service:

8. Prevent P1550-P1551 in Your BMW E90

P1550-P1551 in the E90 is highly preventable with targeted maintenance—especially important for preserving the 3 Series’ legendary throttle response and performance:

• Inspect Air Intake Housing Annually: 2007-2010 328i owners should check for cracks in the intake housing (near MAF sensor) that allow water intrusion. Apply silicone sealant to minor cracks or replace with updated housing (#13717547429).
• Clean Throttle Body Every 30,000 Miles: Carbon buildup on the throttle plate disrupts operation. Use BMW-approved throttle body cleaner (#83122218197) and follow with UR800’s "Throttle Adaptation" to reset calibration.
• Protect Wiring Harness from Heat: Apply heat-resistant tape (3M Super 33+) to harness sections near exhaust manifold—prevents insulation degradation in 335i models with twin turbos.
• Update DME Software Regularly: Use UR800 to check for firmware updates every 15,000 miles. Outdated software is responsible for 15% of false P1550-P1551 codes in E90s.
• Check Battery Health Quarterly: Weak batteries (common in E90s over 5 years old) cause voltage fluctuations that damage throttle actuators. Replace with OEM-spec AGM battery (90Ah) if voltage drops below 12.4V.
• Use BMW-Approved Fuel: Top-tier gasoline (Shell V-Power, BMW Recommended) contains detergents that reduce carbon buildup—indirectly protecting throttle components.
• Inspect Throttle Connector Seals: Apply dielectric grease to the 6-pin actuator connector to repel moisture. Pay extra attention after washing the engine bay (avoid high-pressure spray on connector).
• Perform Throttle Adaptation After Battery Disconnect: Always use UR800 to run adaptation after disconnecting the battery—prevents DME from misinterpreting throttle positions.

9. BMW E90 P1550-P1551 FAQs