Smart Forfour Starting Issues, Bad Ignition Switch Fix

I had a similar starting issue with my 2006 Smart Fortwo last year. Im fairly experienced with basic car maintenance and electronic troubleshooting. Your symptoms match what I experienced, inconsistent starting, rough running and unusual stalling with normal dashboard operation. Initially thought it was the ignition switch too, but it turned out to be a blown fuse in the main ignition circuit. Took it to my regular workshop where they diagnosed and fixed it quickly. They found a damaged 30A fuse in the engine bay fuse box that was causing intermittent power loss to the ignition system. Total repair cost was 52€ including diagnostic and replacement. Before spending money on parts, you should check all fuses related to the ignition system and engine electronics. A faulty fuse can cause these exact symptoms and its an easy fix compared to replacing the whole ignition switch. To help diagnose this further, could you share: Any error codes showing up? Does this happen more often in wet weather? Can you hear the fuel pump prime when turning the key? Are there any other electrical issues? The engine type and transmission details would also be helpful to pinpoint the exact fuse locations to check.

I had a similar starting issue with my 2006 Smart Fortwo last year. Im fairly experienced with basic car maintenance and electronic troubleshooting. Your symptoms match what I experienced, inconsistent starting, rough running and unusual stalling with normal dashboard operation. Initially thought it was the ignition switch too, but it turned out to be a blown fuse in the main ignition circuit. Took it to my regular workshop where they diagnosed and fixed it quickly. They found a damaged 30A fuse in the engine bay fuse box that was causing intermittent power loss to the ignition system. Total repair cost was 52€ including diagnostic and replacement. Before spending money on parts, you should check all fuses related to the ignition system and engine electronics. A faulty fuse can cause these exact symptoms and its an easy fix compared to replacing the whole ignition switch. To help diagnose this further, could you share: Any error codes showing up? Does this happen more often in wet weather? Can you hear the fuel pump prime when turning the key? Are there any other electrical issues? The engine type and transmission details would also be helpful to pinpoint the exact fuse locations to check.

I had a similar starting issue with my 2006 Smart Fortwo last year. Im fairly experienced with basic car maintenance and electronic troubleshooting. Your symptoms match what I experienced, inconsistent starting, rough running and unusual stalling with normal dashboard operation. Initially thought it was the ignition switch too, but it turned out to be a blown fuse in the main ignition circuit. Took it to my regular workshop where they diagnosed and fixed it quickly. They found a damaged 30A fuse in the engine bay fuse box that was causing intermittent power loss to the ignition system. Total repair cost was 52€ including diagnostic and replacement. Before spending money on parts, you should check all fuses related to the ignition system and engine electronics. A faulty fuse can cause these exact symptoms and its an easy fix compared to replacing the whole ignition switch. To help diagnose this further, could you share: Any error codes showing up? Does this happen more often in wet weather? Can you hear the fuel pump prime when turning the key? Are there any other electrical issues? The engine type and transmission details would also be helpful to pinpoint the exact fuse locations to check.

Thanks for the detailed response. Just had my service done at 71971KM, and they didnt spot any ignition system issues then. No error codes showing up at all. The starter motor seems to engage normally when it does work, but the problem is quite unusual. The fuel pump makes its normal sound during key turn. No issues with other car electronics so far. The problem actually seems worse in dry weather, especially after the car sits for a few hours. Will definitely check those fuses first, much cheaper than replacing the ignition switch or other components. Could you point me to which specific fuses I should look at first?

Thanks for the detailed response. Just had my service done at 71971KM, and they didnt spot any ignition system issues then. No error codes showing up at all. The starter motor seems to engage normally when it does work, but the problem is quite unusual. The fuel pump makes its normal sound during key turn. No issues with other car electronics so far. The problem actually seems worse in dry weather, especially after the car sits for a few hours. Will definitely check those fuses first, much cheaper than replacing the ignition switch or other components. Could you point me to which specific fuses I should look at first?

Thanks for the detailed response. Just had my service done at 71971KM, and they didnt spot any ignition system issues then. No error codes showing up at all. The starter motor seems to engage normally when it does work, but the problem is quite unusual. The fuel pump makes its normal sound during key turn. No issues with other car electronics so far. The problem actually seems worse in dry weather, especially after the car sits for a few hours. Will definitely check those fuses first, much cheaper than replacing the ignition switch or other components. Could you point me to which specific fuses I should look at first?

Thanks for the additional details about your Smart Forfour. After you mentioned the dry weather connection, it actually matches my Fortwo experience even more closely. Since the starter motor engages and the fuel pump works, the main 30A fuse is likely fine. You should focus on checking these specific fuses: 15A engine management fuse, 10A ignition control fuse, 20A fuel system fuse In my case, the 15A fuse looked fine visually but had an internal break that would worsen with heat, explaining the dry weather correlation. The fuse would make intermittent contact when cold but fail when the engine bay heated up. The car electronics can still function normally even with a partially failed fuse, which explains why your dashboard and other systems work fine. Before replacing the ignition switch, try swapping these fuses with new ones of identical rating. If new fuses dont solve it, the next step would be testing the ignition switch signal output with a multimeter. A failing switch often shows inconsistent voltage readings during key rotation. This test helped confirm my initial misdiagnosis before finding the actual fuse problem. Let us know what you find after checking those fuses. Its a good starting point before moving to more complex starting issue diagnostics.

Thanks for the additional details about your Smart Forfour. After you mentioned the dry weather connection, it actually matches my Fortwo experience even more closely. Since the starter motor engages and the fuel pump works, the main 30A fuse is likely fine. You should focus on checking these specific fuses: 15A engine management fuse, 10A ignition control fuse, 20A fuel system fuse In my case, the 15A fuse looked fine visually but had an internal break that would worsen with heat, explaining the dry weather correlation. The fuse would make intermittent contact when cold but fail when the engine bay heated up. The car electronics can still function normally even with a partially failed fuse, which explains why your dashboard and other systems work fine. Before replacing the ignition switch, try swapping these fuses with new ones of identical rating. If new fuses dont solve it, the next step would be testing the ignition switch signal output with a multimeter. A failing switch often shows inconsistent voltage readings during key rotation. This test helped confirm my initial misdiagnosis before finding the actual fuse problem. Let us know what you find after checking those fuses. Its a good starting point before moving to more complex starting issue diagnostics.

Thanks for the additional details about your Smart Forfour. After you mentioned the dry weather connection, it actually matches my Fortwo experience even more closely. Since the starter motor engages and the fuel pump works, the main 30A fuse is likely fine. You should focus on checking these specific fuses: 15A engine management fuse, 10A ignition control fuse, 20A fuel system fuse In my case, the 15A fuse looked fine visually but had an internal break that would worsen with heat, explaining the dry weather correlation. The fuse would make intermittent contact when cold but fail when the engine bay heated up. The car electronics can still function normally even with a partially failed fuse, which explains why your dashboard and other systems work fine. Before replacing the ignition switch, try swapping these fuses with new ones of identical rating. If new fuses dont solve it, the next step would be testing the ignition switch signal output with a multimeter. A failing switch often shows inconsistent voltage readings during key rotation. This test helped confirm my initial misdiagnosis before finding the actual fuse problem. Let us know what you find after checking those fuses. Its a good starting point before moving to more complex starting issue diagnostics.

Thanks for the detailed information about the fuse locations and testing procedure. You might be onto something with the heat-related issue. I checked all three fuses you mentioned and found the 15A engine management fuse looks slightly discolored. When I wiggled it, the engine actually started right up. Definitely seems like this could be the culprit causing my ignition problems. Already ordered a pack of the correct fuses, but had a quick question: Should I replace all three fuses you listed while Im at it, since they work together in the ignition system? The parts only cost 12€ total, so it seems worth doing all at once. Also wondering if theres any way to test if the ignition coil might be affected by the faulty fuse before I install the new ones. Dont want to risk damaging new fuses if theres an underlying issue with the coil. Will update once I get the new fuses installed and test the car. Really hoping this fixes the unusual stalling and starting issues without needing more extensive repairs.

Thanks for the detailed information about the fuse locations and testing procedure. You might be onto something with the heat-related issue. I checked all three fuses you mentioned and found the 15A engine management fuse looks slightly discolored. When I wiggled it, the engine actually started right up. Definitely seems like this could be the culprit causing my ignition problems. Already ordered a pack of the correct fuses, but had a quick question: Should I replace all three fuses you listed while Im at it, since they work together in the ignition system? The parts only cost 12€ total, so it seems worth doing all at once. Also wondering if theres any way to test if the ignition coil might be affected by the faulty fuse before I install the new ones. Dont want to risk damaging new fuses if theres an underlying issue with the coil. Will update once I get the new fuses installed and test the car. Really hoping this fixes the unusual stalling and starting issues without needing more extensive repairs.

Thanks for the detailed information about the fuse locations and testing procedure. You might be onto something with the heat-related issue. I checked all three fuses you mentioned and found the 15A engine management fuse looks slightly discolored. When I wiggled it, the engine actually started right up. Definitely seems like this could be the culprit causing my ignition problems. Already ordered a pack of the correct fuses, but had a quick question: Should I replace all three fuses you listed while Im at it, since they work together in the ignition system? The parts only cost 12€ total, so it seems worth doing all at once. Also wondering if theres any way to test if the ignition coil might be affected by the faulty fuse before I install the new ones. Dont want to risk damaging new fuses if theres an underlying issue with the coil. Will update once I get the new fuses installed and test the car. Really hoping this fixes the unusual stalling and starting issues without needing more extensive repairs.