2002 LS1 Cranks But Will Not Start
A bench-side 2002 LS1 no-start path: do the test, compare the result, then take the matching branch. No parts guessing.
Capture codes before you disturb the failure
Connect a scan tool. Crank for about 15 seconds. Record PCM DTCs that fail during this ignition cycle. Then scan the BCM for theft-deterrent codes. Do not clear anything yet.
You have the PCM and BCM evidence from the actual failed start.
Verify the PCM sees cranking RPM
Display engine RPM on the scan tool and crank the engine.
RPM rises above zero while the starter is turning the engine.
Load-check INJR 1, INJR 2 and ECM 1
Key ON, engine OFF. Ground a test light to a known-good ground. Probe both exposed test points on top of each fuse: INJR 1, INJR 2 and ECM 1. That is six checks total.
The test light illuminates on both sides of all three fuses.
Prove spark with a real spark tester
Ignition OFF. Remove one plug wire, install an approved spark tester, keep it away from fuel vapors, then crank.
A strong, repeatable spark jumps the tester during cranking.
Make sure ECT is believable
Before a cold start, compare scan-tool engine coolant temperature with actual engine/ambient temperature. IAT is a useful cold-soak comparison.
ECT is plausible for a cold engine and reasonably close to ambient/IAT.
Command the fuel pump
Use the scan tool output control to command the fuel pump ON. Listen/feel for operation, but treat this only as an operation check.
The pump responds to the command.
Measure fuel pressure while the pump is running
Ignition OFF before installing the EFI gauge at the rail service connection. Then key ON/command the pump and observe pressure while the pump is operating.
The 2002 crank/no-start tree specifies 55–60 psi (380–410 kPa).
Inspect the air path and throttle angle
Inspect the duct between the MAF and throttle body for a disconnected duct or major leak. With the throttle closed, verify the scan data is not showing an obviously open throttle.
The duct is intact and throttle data is plausible at closed throttle.
Use the MAF disconnect only as a diagnostic comparison
If the MAF is suspect and the earlier checks pass, disconnect the MAF and attempt a start. The PCM can use a substitute strategy for this comparison.
The result gives you a clear A/B comparison with the MAF connected versus disconnected.
Inspect plugs and mechanical condition
Inspect spark plugs for heavy fuel fouling. If power, cranking RPM, spark, ECT and fuel pressure all pass, verify mechanical condition/compression and valve timing before considering a controller.
Plugs are usable and the engine has credible mechanical compression/timing.
AFTER THE FAILURE IS PROVEN
Use the proven failed branch—not the original symptom—to choose the replacement. Go from diagnosis to the Parts Verdict →
Before you start
Confirm the page scope above, then work through the published checks in order. Use the linked exact-test procedure whenever this page sends you to one.
Modified car?Check first
This diagnostic path is based on the application shown on this page. If the car has non-stock wiring, calibration, engine-management, fuel-system, cooling-system, security, or other related changes, do not assume the stock path matches the car exactly. Verify the circuit and configuration actually present before using a stock result to condemn a component.
Working on a modified car? Check the modified-car note.
Progress is saved on this device.
Exact tests for this path
Open the full procedure when the diagnostic calls for one, then return here for the next step.
Start here
Follow the tests in order. Use the result you actually get, not the failure you expect to find.
- Confirm this page matches the vehicle and symptom before testing.
- Gather the tools listed on the page before disconnecting anything.
- If a STOP warning appears, do not improvise past it.
- After a repair, repeat the failed test before moving on.
Diagnostic Workpad
Use this as a quick job-side record while you work through the tree. Record what the car actually does before moving to the next branch.
Your notes stay in this browser on this device. They are not sent to F-Body Parts Verdict.
DO NOT REPLACE YET
Do not replace the fuel pump, ignition parts, security components, PCM or sensors just because the engine cranks but will not start. First prove which required input—fuel, spark, injector command, synchronization or enable—is missing.
PARTS VERDICT
Replace only the component/circuit that fails its dedicated test. A no-start is a system state, not a parts verdict.
REPAIR → VERIFY
After repair, verify cold and hot restart, confirm the engine starts without extended crank, and recheck for returning DTCs or loss of the same required input.
FPV DIAGNOSTIC RULE
SYMPTOM → TEST → ISOLATE → PROVE → PARTS VERDICT → REPAIR → VERIFY. A code, symptom or commonly failed part is not proof by itself.