SES light and Diag. Codes [Archive] - TheDieselPage.com Forums

MM9135

09-05-2003, 06:25

My SES light came on a month a go and the code was PO231 low voltage fuel pump circuit. Then it popped on again about a week later and this time it was PO 236, turbocharger boost system. I reset it and it went two weeks and came on again one day and I had it checked immediately and again the PO236. Within a couple of hours the light went out and hasn't returned. The engine (6.5L 1996 3500) starts and runs great all the time (97,000 miles). The only thing I have noticed is the volt meter seems to drop when the AC, wipers and lights are all on which they were the last time the light came on. The rain stopped and the sun came out accessories turned off and the SES went off by it's self. Meter was back to reading 14 volts. When loaded and running at a good speed with all the accessories on the meter will drop to 12.5 Anyone else experience anything like this or do I have a fair weather vehicle? Heh he!

I spoke to a small local shop that rebuilds nothing but alternators and starters and they told me the GM alternator was junk, in those exact words. They showed me an oil drum full of just the copper they salavge from the diode bridges they replace in GM units. They showed me an after market part that is much better built.

Am I on the right track or does anyone think I have a different problem? I just purchased this truck 2 months ago and I am still learning it's quirks.

Thanks

ucdavis

09-05-2003, 10:24

Sounds like you're on the right trail.
DTCs set when a given condition is recorded by the PCM. 0231 sets when the difference between ignition & lift pump voltage is >4 volts. Doesn't mean the lift pump circuit is the cause of the difference, just that the diff is >4V. Since that came once and not since, I'd say you have some other cause of the difference.
Could be in the alternator or in some other draw that is sapping current. @ 97K, looking at the alternator is a good first bet.