P1135 DTC on 2001 Toyota Sienna: Is a 'Stretched Timing Belt' Really Possible?
I own a 2001 Toyota Sienna with over 91,000 miles. I've been experiencing intermittent 'Check Engine' light issues since past 70,000 miles. Recently, after spending $340 to address the P1135 (B1S1) fault code, I also had a timing belt replaced for $224, along with water pump, drive belts, and oil seals—totaling approximately $650 at the same dealership. Minutes after driving, the 'Check Engine' light came back on. I returned immediately and was told the P1135 code reappeared. The technician advised returning next week for repair. Four days later, I returned again and was informed that the system scan tool detected a 'stretched timing belt'—the one installed just four days prior by the same dealer was reportedly one inch too long, and a new belt has been replaced. My question is: Is it possible for a vehicle to generate OBD-II code P1135 due to a timing belt being too long or stretched? Does the Powertrain Control Module (PCM) have a specific diagnostic code for a 'stretched' timing belt? I understand this may sound like I'm overreacting, but if no such code exists in official OBD-II standards, I need clarification from the dealer. Can a vehicle actually run safely with a stretched or improperly sized timing belt? The check engine light is currently off, and the van runs normally—yet I suspect it will come back. I'm seeking expert insight to determine whether this diagnosis is technically valid or if there's a misunderstanding in how P113 or timing belt issues are interpreted.
The OBD-II system does not have a dedicated code for a 'stretched' timing belt. Code P1135 (O2 Sensor Heater Circuit Malfunction) is related to the oxygen sensor heater circuit, not timing belt tension or length. A misaligned or incorrectly installed timing belt could potentially trigger false codes due to PCM relearning issues, especially if the camshaft position sensor readings are affected. However, a stretched timing belt would typically cause mechanical failure or engine damage—such as valve overlap or internal component wear—not a P1135 code. It's possible that the technician misinterpreted the diagnostic result or confused it with another issue like camshaft position sensor malfunction.