1998 V70XC RPMs increase with turn signal during cruise control

wotnartd · Post by **wotnartd** » 28 Nov 2015, 12:04

Okay guys, another weekend, another problem. This time, it's a long winded one. While cruise control is on, and I use a turn signal, the RPMs increase. It doesn't seem to do it below 75mph, and seems to increase by about 200 RPMs. Once the turn signal is off, they drop back down. It does not seem that the speed is impacted. Yesterday, when I applied throttle and used my turn signal, above 75, with cruise on, the change would match the blink. I have not been able to duplicate this.

I have LED rear turn signals, had a bad resistor, removed both resistors. Need to get some glass bulbs again, to properly eliminate them.

Below is a video showing the problem, at no time did I depress the gas, and the road was quite straight and flat.

Scy3iKVhtD8

Thanks, Gang!

Post by **abscate** » 28 Nov 2015, 13:21

The cruise control wires and the turn signal wires run through the switch - my guess is you have broken wires which are shorting together.

Fix this and turn off cruise control until this is done - its dangerous to have uncommanded cruise.

wotnartd · Post by **wotnartd** » 03 Jan 2016, 14:51

Finally resolution! I had still experienced the problem, without cruise on. The surging only occured when the bulb indicator lit, and because I had LEDs with no resistor packs, it was on whenever indicating (even though it was just brake bulbs). I finally remembered to get new incandescent bulbs.

The surging is gone.

But how? How is it the bulb indicator or some other part of the circuit made this happen? I understand I had imparted a resistance fault, but that's it, and only in the rear tails. I never had a change in TPS voltage or position either, as it would surge. So I'm really interested in the how.

Cheers folks! Have a great year.

Post by **abscate** » 03 Jan 2016, 19:17

I'll guess you did not have grounding correct on your LED bulbs. They grounded back through the turn signal switch where I'm guessing they have a common ground with the cruise control circuit...and voila!!

wotnartd · Post by **wotnartd** » 03 Jan 2016, 21:11

abscate wrote:I'll guess you did not have grounding correct on your LED bulbs. They grounded back through the turn signal switch where I'm guessing they have a common ground with the cruise control circuit...and voila!!

It's possible, I suppose. They were just 1156 LEDs and the cruise was off.

Post by **abscate** » 04 Jan 2016, 05:01

Yep, the current from the LEDs turned it back on, even with the switch off. Nasty!

wotnartd · Post by **wotnartd** » 04 Jan 2016, 06:44

Any clue why the PIDs didn't show TPS change?

Post by **abscate** » 04 Jan 2016, 09:18

I don't know the 1998 circuitry very well, but once you start putting signals into the wrong places, all bets are off on 'normal behavior"

I trailer a lot of boats, and when the grounds go bad on the lights, you get all kinds of cool effects in the car from current shunts back to the lighting system.