A frustrating intermittent green key light (immobilizer indicator) on a Honda Odyssey, appearing only under acceleration, was finally resolved after much troubleshooting. This issue arose after a timing belt failure repair. The engine had seized at 70mph due to a tensioner failure, requiring head removal and valve replacement. Initial attempts to jump-start the vehicle were unsuccessful, resulting in only a clicking sound and dimming lights.
While working under the hood, a closer inspection revealed a damaged negative battery cable. A four-inch section of exposed copper wire near the transmission bolt terminal showed significant discoloration and a powdery residue. Although the cable seemed securely connected, manipulating the strands revealed its compromised condition.
Prior to this discovery, all battery, body, and PCM (Powertrain Control Module) grounds had tested good. However, considering the forceful attempts to jump-start the seized engine, it’s plausible the ground cable suffered damage, leading to increased resistance under load, particularly during acceleration.
The theory is that this higher resistance, exacerbated by flexing during acceleration, caused signal grounds within the PCM to float above 0V. This fluctuation potentially disrupted communication within the system, triggering the immobilizer indicator light. Importantly, all PCM ground wires share a common point within the module. Therefore, accurate continuity testing requires disconnecting each wire from the PCM.
Replacing the damaged negative battery cable completely eliminated the intermittent green key light issue. This suggests the damaged cable was the root cause, highlighting the importance of thoroughly inspecting ground connections, especially after significant engine work or jump-starting attempts. A seemingly minor cable issue can lead to perplexing electrical problems and trigger the Honda immobilizer system. This case underscores the critical role of proper grounding in maintaining a stable electrical system and preventing erroneous activation of the immobilizer system.
