Problem Description:
I own a 1994 automatic trans Camaro Z28 (LT1 engine) with about 88,000 miles on it. The problem is that the “Service Engine Soon” lights up and the fan comes on after driving it for about 2 to 5 minutes. I was told that the car is showing trouble codes 28 and 29 (ODB 1). If the car is stopped (such as at a stop light) for about 5 to 10 seconds while the engine is running, the “Service Engine Soon” turns off along with the fan. The “Service Engine Soon” light and the fan will come back on again no more than 5 seconds after the car begins to move again. Also, if the car is in park and the “Service Engine Soon” light and the fan is off, they both will come on if I keep the engine at about 2,000 RPMs even while the car is in park. Other than the “Service Engine Soon” light and the fan coming on with it, there doesn’t seem to be any other problems. What could be causing the “Service Engine Soon” and the fan to turn on? I appreciate any suggestions.

Background:
I replaced the thermostat with a 180F Stant 14218, installed a K&N 5730101 cold air intake, and changed the transmission fluid. Afterwards, the transmission wasn’t shifting properly even though the fluid level was good (there were no noticeable transmission problems before this), so I took my car to a transmission specialist to see what was wrong. I drove it approximately 100 miles between the time I changed the thermostat, air intake, transmission fluid change, and the time I took my car to the transmission specialist. Of course, the transmission specialists claimed to have found a lot of problems with the transmission and charged me a ton of money to fix it. The “Service Engine Soon” never lit up until after I got my car back from the transmission specialists. I drove my car between 20 and 30 miles after I got it back from the transmission specialists before the “Service Engine Soon” light came on. So, I took my car back to the transmission specialists since they were the last people to make any changes to my car before the “Service Engine Soon” light came on. After the transmission specialists replaced a lot of the same parts again and did some tests, they came to the conclusion that the “Service Engine Soon” light had nothing to do with the transmission. They thought the cold air intake might have something to do with the problem. According to the transmission specialists, the trouble codes being generated were 28 and 29. The code description they wrote down for me read code 28 = “manifold pressure” and 29 = “secondary air pump.” According to my Haynes Repair Manual, code 28 = “Transmission Range – Check transmission control circuit” and code 29 = “Secondary Air Injection – Check the Secondary Air Injection (AIR) system electrical circuit in the wiring.” The transmission specialists suggested I take my car to an auto mechanic they knew who was good at troubleshooting problem codes because other auto mechanics would probably blame the transmission for the problem. After I got my car back from the transmission specialists, I disconnected and then reconnected the air intake, along with all of the associated wires and hoses. I also removed my gas tank cap and screwed it on again, since I heard that was a commonly overlooked cause of the “Service Engine Soon” turning on. Finally, I unplugged the car battery and plugged it back in. None of these actions fixed the problem. I also attempted to double check the trouble codes at two different auto stores that scan for free, but two different scanners displayed, “Not Responding.” I also tried one of the cheap scanners that cause the “Service Engine Soon” light to flash and pause, but it didn’t work either. If the problem has something to do with the cold air intake or new thermostat, then why didn’t the “Service Engine Soon” light come on immediately after I replaced those items? Is the transmission specialist at fault?

 

Code 28-Transmission Range
Check the transmission range control circuit

Code 29- Secondary Air Injection
check for an open circuit

 

Code 29 usually means your air injection pump (drivers side of the engine, about half way down, black plastic and about 5-6 inches round, about 4 inches long, has a tube that goes into the the drivers side exhaust manifold), if it hasn't been covered by the recall, then you can take it to a dealer and they will replace that for free. The other one I would say has something to do with the electronics in the tranny or possible the PCM controlling it. I would check for loose connections to the tranny and then if nothing, take it to another tranny shop, one with a really good rep and have them look at it, might cause you some money, but if it does and the tranny is the problem, then the first tranny shop owes you that money.

 

I appreciate the responses - thank you. Since greenarrow said my air injection pump may be covered by a recall, I called the Chevrolet customer assistance center at 1-800-222-1020 to see if my car was eligible for any recalls, but it was not. I located the air pump recall diagram from Shoebox's page (http://shbox.com/1/air_pump_recall.jpg), yet I could not find anything official (i.e. a recall id number or a technical service bulletin - TSB). As far as I can tell, all of the connections relevant to the air pump and transmission appear to be intact. I explained the issue to an auto mechanic in the area who received good internet reviews and also does transmission work. My appointment is on 17 Mar and I will show Shoebox’s air pump recall diagram to the auto mechanic. If anyone reading this knows of a TSB or recall ID for the air injection pump, please let me know what it is. Thank you.

 

hey,just a long shot but my ses light came on and when i hooked my code reader to it was dtc29.fans came on and went into open loop after about 3-4 minutes everyday.did as much research as i could for a couple weeks.finally checked the fuse under the hood for secondary air system and it was blown.changed and ses light went out and closed loop again.just a long shot but worth looking at.be sure to check the fuses under the hood.good luck

 

Problem fixed-

I replaced both the secondary air pump and the oxygen sensor and it did not fix the problem. The last auto mechanic I took my car to said these were the two parts that were causing the service engine soon light and the radiator fan to come on. This recommendation was also consistent with what many other people thought as well, but this didn't work. Then, I took Dave's (dc14u2no) advice and checked the fuse. The problem wasn't that the fuse was blown. The problem was that there was no fuse at all!!! I took one of other fuses with the same voltage (20 Amps) and put it in the air pump slot. It fixed the problem. Thank you, dc14u2no.

It makes me wonder who removed the fuse. The transmission place that rebuilt my transmission wasn't the first place I took my car to. I brought my car to a transmission specialist so they could diagnose the problem. Then, I found a second transmission specialist who quoted me $500 less. So, I told the first place not to do any work and I picked up my car from them and brought it to a second transmission place. It turns out that the owners of both of these transmission places were friends and the second one called the first one to tell him I was taking my car to him because he charged less. After my SES light came on, I brought my car back to the second transmission place since they were the last ones to work on my car before the SES light came on. The second transmission place wanted me to bring my car to their auto mechanic friend who was good a trouble-shooting SES codes. Given that the SES light did not come on until after I got my car back from the second transmission place, the fact that they wanted me to take my car to their friend to fix it, and the fact that the fuse couldn't have fallen out by itself since it is sealed in a box makes me suspect nefarious business..but I don't know for sure.

 

Glad it worked out for you.Mine was driving me crazy.Now if I could get my other issues fixed.Might throw out some questions in another post.Vo Dave