The Problem: Vacuum Assist
Your brake booster uses engine vacuum to assist in braking. When you apply the brakes, it pulls vacuum. If the engine stalls, it's likely losing vacuum, causing the brakes to feel very hard and possibly leading to the stall.
Possible Causes:
* Vacuum Leak: This is the most common culprit. A leak in the vacuum lines connecting the intake manifold to the brake booster can cause a loss of vacuum. Check all lines for cracks, holes, or loose connections. Pay close attention to the line near the booster itself.
* Brake Booster Failure: The booster itself might be failing, unable to hold or utilize the vacuum properly. This requires replacement.
* Intake Manifold Leak: A leak in the intake manifold will also reduce vacuum throughout the system. This is a more serious problem and requires more specialized diagnosis and repair.
* Power Steering Pump (Less Likely): While less common, a failing power steering pump can sometimes affect the vacuum system (depending on the year and model's design). Check the power steering fluid level and for any leaks.
* Dirty Air Filter: A severely clogged air filter can restrict airflow and affect engine performance, potentially leading to stalling under load (like when braking). It's a good idea to check this anyway, as it's a cheap and easy fix.
* Other Engine Issues (Less Likely): While less likely to be the *direct* cause of stalling *only* during braking, underlying engine problems (like ignition issues, fuel delivery problems) could contribute if the engine is already running weakly.
Troubleshooting Steps:
1. Check the Brake Booster Vacuum Line: This is the easiest and most likely place to find the problem. Visually inspect the line from the intake manifold to the brake booster for any cracks, loose connections, or damage.
2. Listen for Leaks: With the engine running, carefully listen around the brake booster and vacuum lines for hissing sounds, which indicate a vacuum leak. Use a spray bottle with soapy water; spraying around suspected leak areas will show bubbles if there's a vacuum leak.
3. Check the Brake Pedal: With the engine *off*, repeatedly pump the brake pedal. If it takes many pumps to build up pressure, and then holds that pressure, this indicates the booster is likely okay. If it immediately goes to the floor with very little resistance, it likely points to a failed brake booster.
4. Inspect Air Filter: Replace the air filter if it's dirty or clogged.
5. Check Engine for Other Issues: If the above steps don't reveal the problem, have a mechanic perform a more thorough diagnosis of the engine's overall health.
Important Note: If you suspect a vacuum leak or brake booster problem, avoid driving the car extensively. The lack of proper brake assist makes the vehicle unsafe.
If you're not comfortable performing these checks yourself, take your Saturn SL2 to a qualified mechanic for diagnosis and repair. Be sure to describe the problem precisely — that the engine stalls *only* when the brakes are applied. This helps them focus their diagnosis.
