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GMC Forum: 1999 GMC Sonoma weird starting problem
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  #1  
Old 01-08-2010, 03:24 PM
DaShiznit DaShiznit is offline
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Default 1999 GMC Sonoma weird starting problem

My 1999 GMC Sonoma (just bought used... 115,000 miles) has this strange problem that it will only start when I turn the key to the on position and the headlights come on without the headlight switch in the on position. Both the headlights and taillights are on, and the truck starts fine. However, recently the starter died and I had it replaced. Now the headlights are not coming on at all when I turn the key to the on position and the truck will not start. I don't think it's normal for the lights/taillights to come on with the switch off, but truck has started fine like this since I got it. I first thought they were daytime running lights, until I got out and saw the taillights on too. Battery is brand new and fully charged.

This problem was sporadic, but now the headlights will not come on at all when I turn the key to the on position (before I could turn the key on and off many times... eventually the headlights would come on, with the headlight switch in the off position, and the truck would start).

My AAA ran out (I used up all 4 tows this year... ouch!) and it will cost me over $175 to get it towed to the garage. If anyone has an idea to allow me to get it started just so I can drive it to the garage to have it diagnosed that would be awesome! Thank you.
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Old 01-08-2010, 08:38 PM
epiphaknee epiphaknee is offline
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It sounds like your ignition key lock cylinder is bad. Can you remove the key even when the cylinder is turned to one of the functioning positions? I would be tempted to try and replace the cylinder. That repair is not too difficult and the Shop Manual has a good writ-up on how to replace it. With an auto, it is 15815961. That is about $38.00 before shipping at gmpartsdirect.com But it might not solve the problem. However, that would get you into the steering column and then you could look for other electrical problems.

However, 1999 is known to have strange wiring situations that occur at the same place right there in the steering column. Is you hazard switch broken by chance? Does your multi-function switch work - cruise, blinkers, wiper cycle?

As far as towing goes, on your auto insurance you can for about $4.00 every six months obtain a towing service. So that might be a way to bridge the gap with AAA by changing your auto policy.
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Old 01-10-2010, 12:58 PM
Molson02536 Molson02536 is offline
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There are five main contacts in the switch. These contacts control everything in the truck. For instance, the large brown wire in the middle/top portion of the switch is the accessory power wire which feeds into the RAP (retained accessory power) relay then off to all the accessory items (radio, windows, etc). The large orange wire is the IGN 3 wire which powers the ABS, HVAC, 4WD, and cruise systems. The large pink wire is the IGN 1 wire that powers the ECM, ENG 1 fuse, O2 sensors, B/U lamps, DRLs, A/C relay, etc.

On the other side, you have the small white wire which feeds the IGN 0 circuit (cluster) and the small yellow wire which feeds into the starter circuit. These two items get power from the small red wire (IGN C fuse) when their respective contacts connect.

Here is a run down of what circuits have power for a given key position (ACC, LOCK, OFF, RUN, & START):

* IGN 0 (small white wire) circuit has power in OFF, RUN, and START
* CRANK (small yellow wire) circuit only has power in START
* ACC/RAP (large brown wire) circuit has power in ACC and RUN
* IGN 1 (large pink wire) circuit has power in RUN and START
* IGN 3 (large orange wire) circuit has power in RUN only

Since some of the circuits can have a fairly high current load on them when you start your truck, the arc that happens when the contacts close can be pretty intense. Over time, the contacts will erode/corrode and will loose their conductivity to each other, usually in the form of a higher resistance. This higher resistance also causes heat which further exacerbates the problem.

The IGN 3 contacts are the most heavily loaded of all of the contacts in the system and it also is the contact which is opened and closed the most during the life of the truck. Lets look closer at what this contact goes through on a normal start sequence. In a typical start cycle, the key is turned from LOCK, through OFF and RUN, then to START, and finally back to RUN once the vehicle is started. As the key is turned from LOCK to RUN, the IGN 3 contacts close. When the key is then turned to START, the contacts open back up. Once returned to RUN, the contacts close again. This is why it is vitally important to hold the key in the START position until you are sure that the engine is running. The more times you go to the START position, the more life you take away from these contacts.

For the 98+ trucks, the most common issue is the "security" light on the dash illuminating. But the problem can also manifest itself as an inoperative fuel pump, unresponsive cluster, ABS and/or SIR lights being illuminated on the cluster, as well as a no start condition (either related to the inoperative fuel pump or a failure of the starter to turn over). The ignition switch can also cause PASSLOCK issues.


Hope this helps you understand more what epiphaknee has mentioned. Great work epiphaknee.
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Old 01-10-2010, 09:27 PM
DaShiznit DaShiznit is offline
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Quote:
Originally Posted by epiphaknee View Post
It sounds like your ignition key lock cylinder is bad. Can you remove the key even when the cylinder is turned to one of the functioning positions? I would be tempted to try and replace the cylinder. That repair is not too difficult and the Shop Manual has a good writ-up on how to replace it. With an auto, it is 15815961. That is about $38.00 before shipping at gmpartsdirect.com But it might not solve the problem. However, that would get you into the steering column and then you could look for other electrical problems.

However, 1999 is known to have strange wiring situations that occur at the same place right there in the steering column. Is you hazard switch broken by chance? Does your multi-function switch work - cruise, blinkers, wiper cycle?

As far as towing goes, on your auto insurance you can for about $4.00 every six months obtain a towing service. So that might be a way to bridge the gap with AAA by changing your auto policy.
I just checked the truck and you are right epiphaknee. The key comes out when in the run position. When I checked the truck, the lights came on again with the light switch in the off position. I thought, excellent, at least I will be able to get the struck started this time and drive it the 20 miles to the garage... alas, it would not start.

The battery is still fully charged (it's a brand new Interstate) but repeated turns to the start position did nothing. A friend mine is going to call AAA with his extended service plan and get the tow for me tomorrow and I hope the garage can fix it on the cheap with both your suggestions, epiphaknee and Molson02536. I thank you for your help, and will post what the garage does (or wants to do) to fix the problem.

Thanks again.

DaS
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Old 01-11-2010, 11:46 AM
DaShiznit DaShiznit is offline
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I just checked the truck and you are right epiphaknee. The key comes out when in the run position. When I checked the truck, the lights came on again with the light switch in the off position. I thought, excellent, at least I will be able to get the struck started this time and drive it the 20 miles to the garage... alas, it would not start.

The battery is still fully charged (it's a brand new Interstate) but repeated turns to the start position did nothing. A friend mine is going to call AAA with his extended service plan and get the tow for me tomorrow and I hope the garage can fix it on the cheap with both your suggestions, epiphaknee and Molson02536. I thank you for your help, and will post what the garage does (or wants to do) to fix the problem.

Thanks again.

DaS
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