My Check Engine Light has come on recently and I am not sure what the problem is. I am getting codes 21, 51, 52. The CEL is usually on quite bright in the morning, after the truck sits all day at work I can still barely see the CEL light on. Does the intensity of the light mean anything? I get the same codes either way.

The truck runs ok for the most part, but sometimes in the morning or when really damp it hesitates real bad from 1500-3000RPM then it "kicks in" and has full power. This usually goes away once the truck has run for 15 minutes or so. From reading some of the other posts it seems like this could be EGR related but none of these codes say that. Am I correct that the EGR can get built up with carbon deposits and can be cleaned with Tbody cleaner?

I know that 21 is O2 sensor but I have replaced that about 3 months ago.

52 is Knock sensor, where do I find the knock sensor on an 87 4runner 22re?

51 is AC Signal on: DL contact off. What is the DL contact?

Also, does anybody know what this sensor is. It is in the Thermostat housing. I have looked on an 89 and a 95 and neither of those have the sensor??? Is this the knock sensor? I have a Haynes manual and there is no mention of the knock sensor in there nor in the online 93FSM.

 

that is your coolant temp sender for your dash guage. the knock sensor is under your intake on the block. the 51 is a kind of vague code, idl signal, park nuetral switch, ac amp signal ??? the idl signal is dealing with the throttle position sensor, i had that code and i believe the tps took care of it.

 

I forgot to mention that I also have adjusted my TPS and it seems to be fine. There used to be AC in the truck but it has been removed. It was gone when I bought the truck?? Compressor removed and hoses are cut. Has been like this for 2 years since I have owned it and no CEL til now.

 

kind of tedious but very straight forward way of pinpointing the problems is to probe your computer with a multimeter. if you want i can scan the pages from my manual the values i believe will all be the exact same between 87 and 89.

 

no, that sensor is the A/C thermo switch.
the gauge sensor is locaked farther back, on top, with a single connector. about right next to the intake valve.

 

as for your 51 code, DL contact is a pressure switch for your high and low side of the A/C. your computer is confused. it is being told the the A//C sould be on, and cant turn on cause the pressure switch is open. disconnect the plug from the A/C thermo switch. this might make your code go away. or you could replace the sensor. but w/o A/C hooked up, seems like a waste of $$$

 

the knock sensor was just described to you where its located. but whats important about that sensor, is it uses a coaxial cable. this means it has a RF shield that surrounds the conductor wire. if this shield is damaged, RF can enter, or leak, and signal is distorted. chek the integrity of wire.