The engine catches, it runs for a second or two, and then it dies like someone turned a switch off. You can repeat that all morning. It never stays running long enough to drive out of the driveway.<\/p>\n
That pattern is specific. A dead battery usually will not start it at all. A failed starter does not get you a firing engine. Something allowed fuel and spark for a moment, then took them away. On a lot of vehicles that something is the ASD relay dropping out, a security system that never approved the start, a crank signal that vanished, or a PCM that shut the engine down.<\/p>\n
This blog covers why a car starts and then dies, how to tell those causes apart, and when the computer is actually the part that quit.<\/p>\n
If the engine starts and then dies, it usually had fuel and spark for the first second and lost one of them right after. On Chrysler-family vehicles the ASD relay is designed to drop if it does not see a valid crank signal or a security approval. Other makes use a main power relay that behaves the same way.<\/p>\n
Check whether the fuel pump keeps running, whether the security light is doing anything, and whether a scan tool can see RPM while it cranks and dies. Those three observations split most cases before anyone prices a module. Related reading: P0685 code meaning<\/a> for the power-relay circuit, and no injector pulse while cranking<\/a> if it never fires a second time.<\/p>\n Use the first two seconds of run time as data. What stays alive and what drops out tells you the cause.<\/p>\n The ASD or main power relay often closes for a moment at key-on, then stays closed only if the PCM keeps commanding it. If the relay, its fuse, or the control circuit fails, the engine can fire off residual fuel and die as soon as that feed drops. You may hear the relay click off right when the engine quits.<\/p>\n Swap the relay, check the fuse, and measure power at an injector or coil while it dies. If voltage disappears at the same instant the engine stalls, stay on this circuit. P0685 is the code that often rides along.<\/p>\n An immobilizer can allow a brief start and then shut the engine off when the key is not approved. The security light flashing or staying on is the giveaway. This is the SKIM pattern on Jeep, Dodge, and Chrysler, covered in SKIM no start<\/a>.<\/p>\n Try a second original key before you replace a relay or a computer. A security cutoff can look exactly like an ASD dropout because the PCM is the one that opens the relay on purpose.<\/p>\n The PCM needs a crankshaft signal to keep the engine running. A weak sensor or a damaged tone ring can provide just enough signal to start, then drop out as soon as rpm changes. The engine dies, and a second crank may show no RPM on the scan tool.<\/p>\n Watch live RPM during the start-and-die event. If the reading falls to zero while the engine is still spinning down, the sensor or reluctor is the suspect. That is a signal problem, not a guess at the PCM.<\/p>\n Some vehicles prime the pump at key-on, start on the fuel that is already in the rail, then die when the pump never stays powered. On Chrysler products that feed often runs through the TIPM. A failing relay inside the module can produce a clean start-then-stall with no other warning.<\/p>\n Listen for the pump after the engine fires. If it goes quiet when the engine dies, test power at the pump and at the TIPM output. The TIPM module<\/a> article walks through that failure style.<\/p>\n When the relay stays closed, the pump keeps running, the security light is happy, and RPM stays visible while the engine dies, look at the PCM. Internal faults can cut injector or coil drivers a second after startup. That lines up with other bad ECM symptoms<\/a> such as random stalling or a module that communicates only part of the time.<\/p>\n Confirm power and ground at the module during the stall, not just with the key on and the engine already dead. A supply that collapses under load can imitate a failed computer.<\/p>\n Watch the pump, the security light, and the RPM reading at the moment it quits.<\/p>\nCommon Causes When It Dies After Starting<\/h2>\n
1. ASD or Main Relay Dropout<\/h3>\n
2. A Security System Cutoff<\/h3>\n
3. Crank Signal Loss After Startup<\/h3>\n
4. Fuel Pump or TIPM Power Loss<\/h3>\n
5. A Failing PCM<\/h3>\n
How to Tell Start-Then-Die Causes Apart<\/h2>\n