Bituman

When I start my car the interlock warning light is on. It's the red light that is above the oil pressure gauge that looks like an "H". After the car goes over about 10 mph, the light goes out and never comes on until the next start. It may be my imagination, but I think the light comes on more so after cold starts. In other words, there are times when it doesn't come on at all. I searched the forum and found this thread, but the symptoms described there are not exactly the same as mine. I am getting no warning buzzer and no ABS light.

Any ideas would be much appreciated. Thank you.

Bob

Southampton76

Did you change the brake fluid? Check the fluid level as this sometimes causes problems. You have a C4, try putting the locking the diff on, does the small light go on in the centre console? If it does, drive it, does it feel tough to drive, if so the diff is OK.

I had the brake light and diff interlock on every now and again. I replaced the brake fluid level sensor and it went away.

Mark

Bituman

Thanks Mark, I'll give that a check. The threaed I referenced also talked about brake fluid level, so you are probably right. BTW, the small amber light on the center console is also on when the red interlock light is on. But they go out at the same time. I am obviously hoping this is no big deal!

Bob

Southampton76

Might be connected to the ABS pump, mine goes on at start-up and will go out right away or after you get going. To be honest, I really don't pay attention to the start-up sequence now unless a light stays on or comes on. Which doesn't happen often. All my dash "lights" have been related to the brake fluid level.

Bituman

Well that's two votes for brake fluid plus the previous thread suggested same. Thank you again.

Bob

Bill Wagner

It's completely normal for the lights to come on after startup for up to 30 seconds. Have you tried the following:

1. Start the car, watch the lights, they should be on.
2. Wait about 10 - 30 seconds. They should go out on there own.

If they don't go out on there own, something is wrong. If they do go out on their own, it's normal. Note that this will generally only happen after a cold start. The system needs to pressurize. Once pressurized it will generally remain that way for several hours after the cars been turned off. For example, if your car sat overnight, it will need to charge up fully. If you stop at a store, go in for an hour, and come out, it will charge only briefly...like a few seconds.

Bituman

Thanks Bill for the ideas. For sure the interlock light does not go out after about 30 seconds just sitting there idling. But I can't remember how long I've let the engine idle before pulling away. So maybe I'll try letting it go a little longer. As I mentioned above, the light goes out almost immediately when I pull away. I'm travelling this week so I have not had any more chance to figure this out.

But I did review Streather's book (pp. 396-399) in the meantime and there is nothing there that has symptoms like mine. On pp. 223 he mentions one situation when the interlock will light up "only initially." That is, when hydraulic pressure reaches 115 bar but no more. However, in that situation he mentions that brake application will cause an ABS light too. Basically all the typical problems with an interlock light also include an ABS light, which I do not have.

As mentioned in the post above, I want to try locking the system to see if it is mechanically working. That's a feeling I know from my old Bronco and the Detroit lockers I have. Thank you again Bill.

Bob

c4randyr

I have a bit of a different spin on the interlock light issue. My interlock and brake lights go on when the car is started, but soon go off. Lately, 15-20 minutes into my commute to or from work, the lights go on and stay on until the ignition is switched off and on again. Any ideas on what might be causing this behavior?

Randy R.

Southampton76

I had the same problem. It was all related to brake fluid level and the sensor.