While etc (Electronic Throttle regulate or Drive-by-Wire) could sound like a an excellent idea in theory, both the practice and also execution often leave every little thing to be desired, and specifically so top top Jeep vehicles- as this write-up will recount. You may have battled battles through the etc system ~ above Jeeps before and also you may also have won several of them, however in the situation of the Jeep vs.

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the three young and also inexperienced chrischona2015.orgs that we featured right here a few weeks ago, a Jeep cool Cherokee and also its ASD relay-controlled etc system to be the clean winners- and by a vast margin, too. In this article, we will certainly recount the pertinent points of the case, and explain how it was addressed with the usage of one old sealed beam headlight, however let us begin by stating-

The problem

We need not repeat the history of the 3 young chrischona2015.orgs here, past saying that a) lock pooled their resources soon after ~ qualifying as chrischona2015.orgs, and b), that they supplied their pooled resources to open up a little workshop many years prior to they were prepared to accept occupational from payment customers. We can additionally say that based upon their reasonably recent suffer with failing to diagnose a basic misfire correctly, they admitted defeat at an early stage in the battle, and chose to call in a consultant: this writer, to it is in exact. Here are the facts of the case-

The car was a 2010 Jeep cool Cherokee whose engine cranked and started normally yet only ran for two seconds or so before shutting off. It would certainly restart immediately, but only if the ignition to be turned off chrischona2015.orgpletely before restarting. Attempting to start the engine without an initial turning turn off the ignition caused a no-crank condition.

According chrischona2015.orge the three young chrischona2015.orgs, that wrote considerable report top top the symptoms and background of the difficulty as it to be recounted to them by vehicle’s owner, the engine very first started cutting out sporadically if diving about 3 month ago. In ~ first, it occurred sporadically and also unexpectedly under every weather conditions, throughout most steering conditions, and at virtually all engine speeds, engine loads, and ambient temperatures. In short, there was no discernible pattern to the engine cut-outs, but it would always restart if the ignition was an initial turned off.

After a few weeks, the problem became worse in the sense that the engine would certainly shut down at the very least once during each chrischona2015.orgmute between the automobile owner’s home and office. In ~ this time, a dealership changed the ECU and also various sensors, consisting of the crank place sensor, engine coolant sensor, and also a chrischona2015.orgponent of the engine wiring harness. Follow to the vehicle’s owner, the dealer might find no trouble codes once they had actually the vehicle, however despite your assurances (and an eye-watering repair bill) the his Jeep would now be "like new", the opposite happened. The trouble got steadily worse till the vehicle had end up being undrivable a couple of days before.

To their credit though, the 3 young chrischona2015.orgs believed of connecting a high-end scan tool, albeit a non-Jeep-specific scan tool, and managed to record a solitary trouble password after countless attempts to record live data and freeze framework information during the two seconds they had at their disposal. The password was P2100, which is many chrischona2015.orgmonly defined as “Throttle Actuator "A" control Motor Circuit/Open”, although the is sometimes defined as “Throttle Actuator control (TAC) Motor regulate Circuit”, depending on the resource consulted, i beg your pardon brings united state to what the young chrischona2015.orgs did not recognize -

About extracting error codes on Jeeps

Nobody knows everything, however sometimes the helps once you know what you don’t know. In this details case though, the three young chrischona2015.orgs’ collective lack of expertise was so substantial that they could not minimize the difficulty to its easiest form, which to be the fact that the Jeep did not start because there was a difficulty with the digital throttle control system.

However, in the attention of fairness, it should be stated that Jeeps use a quite convoluted start-up logic the is largely unique to Jeeps, but more importantly, the Jeep has actually never released all the fault-setting criteria for also generic ETC-related trouble codes. Also, while some ETC-related trouble codes will collection immediately as soon as the vehicle fails to start, many of these codes space erased immediately when the ignition is turned off and also an on in ~ a few seconds. Thus, the practical effect of these merged strategies is that in numerous cases, the is all yet impossible chrischona2015.orge extract some fault codes and also their related freeze frame data if a Jeep’s engine does no run for an ext than 5 seconds.

Therefore, in the real world, many experienced technicians diagnose and resolve no-start conditions on Jeeps v the understanding they have got over plenty of years. Placed differently, this method that if girlfriend are faced with a no-start problem on a Jeep, Google is not necessarily your friend, i beg your pardon begs the inquiry of-

How the start-up logic on Jeeps works



Before we obtain to specifics, it could be worth noting the all vehicles that space made and also sold in the USA (including vehicles imported right into the USA) are legally forced to have a mechanism that automatically shuts down the fuel supply* in some situations, together as mishaps or severe results to prevent fuel fires.

*Note the while this need does not apply to part markets, this feature is generally retained top top Jeep vehicles that are produced in the USA and then exported to foreign markets.

This is intended together a safety feature, and while many OEM manufacturers regime this role directly into the ECU, Jeep, top top the other hand, chosen to usage an ECU-controlled electro-chrischona2015.orgal 12V relay to both supply power to the fuel pump, injectors, and also ignition coils during normal automobile operation, and also to cut power to these systems when the instance demands that power be cut.

In Jeep-speak, this relay is known as the ASD relay (Automatic Shutdown Relay), and also this relay is almost invariably the cause of no-crank and/or no-start problems on all OBD II chrischona2015.orgpliant Jeeps. Also, and also to do the start-up reasonable on Jeeps even much more “clunky”, the ASD relay additionally supplies power to the electronic throttle regulate actuator. In practice, this method that unlike many other car makes on i beg your pardon the and so on system typically does not share circuits with anything else, issues in one or an ext circuits that space not straight related chrischona2015.orge the and so on system can, and often do, disable the and so on system.

We stated the chunkiness of the start-up logic of OBD II Jeeps earlier, and while the actual process is as well long and convoluted to describe it in fine information here, we have the right to do the next finest thing, which is to provide an rundown of the 8 points that must happen (or it is in present) to prevent the ASD relay from "dropping out", for this reason cutting strength to the fuel and also ignition systems-

1) The battery optimistic terminal top top the relay must have actually a minimum that 12 volts on the at all times

2) The ECU offers the ignition coils" major circuits together a feedback system to identify the intensity of the ignition sparks. Therefore, if the primary existing is weak or missing on the ignition circuits, the ECU will conclude that there are problems in the ignition system, and it will certainly disable the ASD relay as a result.

3) If the crank position sensor is defective, or produces erratic signals, the ECU will disable the ASD relay.

4) If the camshaft place sensor is defective, or produces erratic signals, the ECU will certainly disable the ASD relay.

5) If the ECU detects a miscorrelation in between the signal from the crankshaft and camshaft place sensors, it will certainly disable the ASD relay.

6) If any output ~ above the ASD relay falls listed below a minimum allowable threshold, the ECU will conclude that the relay is defective, and it will disable the relay as a result. Note though the Jeep has never released the value(s) of these minimum allowable thresholds.

7) If any kind of immobiliser-related faults are current or if the ECU detects worries with programming and/or security codes in ignition keys, it will disable the ASD relay.

8) note that on part late-model Jeeps, the fuel pump is managed by a dedicated relay in enhancement to the ADS relay that controls power to the injectors and also ignition coils. Thus, the ECU monitors the output of the fuel pump relay, and if this output falls below a minimum allowable threshold, the ECU will certainly disable both the fuel pump relay and also the ASD relay.

While the above sounds reasonable enough, the difficulty is the a) all of the over conditions need to be met throughout the very first two secs of cranking, and b), no faults should be detected within the an initial two seconds of cranking because that the engine to start and also run. Moreover, in part cases, some types of intermittent electric failures in one or much more circuits can cause the ASD relay to “drop out” intermittently or sporadically, bring about intermittent, sporadic, and unexpected engine stalls. In numerous instances, this intermittent failures take place without a discernible pattern, together the owner that the problem Jeep grand Cherokee had actually reported, i m sorry brings us to-

ASD relay diagnostics

When this writer questioned the 3 young chrischona2015.orgs about what diagnostic actions they have actually performed to find the problem prior to calling because that help, it soon came to be clear that they had only the vaguest of principles of what is forced for a chrischona2015.orgmon Jeep petrol engine chrischona2015.orge start and also run.

Nonetheless, all knowledgeable chrischona2015.orgs will certainly recognise the it could take several hrs to verify the all eight factors that make up the start-up logic of Jeep engines are within acceptable parameters, however there is one easy way to limit the feasible causes the a no-start condition on Jeeps. Long experience through Jeeps has taught the scoping the 2 circuits that manage the movement* of the throttle plate via the stepper engine is usually the quickest method to create useable diagnostic data and/or clues, therefore the first step was to affix a digital warehouse scope chrischona2015.orge the throttle actuator.

* top top Jeeps, the ECU switches the actuator motor’s polarity chrischona2015.orge open and close the accelerator plate, and two dedicated position sensors are offered to screen the actual place of the throttle plate loved one to the desired or chrischona2015.orgmanded position.

The image below shows the results of the test, i m sorry is a 2-second record with one lead connected to one live terminal, and another lead associated to the other live terminal in the accelerator actuator’s connector. The ground link was referenced directly to battery negative-


Image source: https://www.searchautoparts.chrischona2015.org/sites/default/files/images/FIG4%20copy_0.png 

Note that as soon as the ignition to be turned on and light push was put on the throttle pedal, the red trace sees 12 volts, but practically immediately, the green trace likewise bechrischona2015.orges active- additionally at 12 volts. Keep in mind the chaotic switching between the two circuits; this is clear proof of the ECU make the efforts to switch the actuator motor"s polarity in an attempt to exactly what it interprets together a stuck throttle plate.

Note, however, that the chaotic switching in between polarities wake up at a substantially reduced voltage, which could mean among three things. The first is the an abnormally high resistance in between the ASD relay (which provides the etc with power) is reducing the existing that reaches the ETC; the second is that the ASD relay itself might be defective in a method that affect its output to the ETC, and also the third is the there is a difficulty with the ECU or v the circuit between the ECU and also the ASD relay. Together a useful matter, remember the the ECU monitors the ADS relays’ output, which in this case, to be substantially listed below 12 volts once the engine to be cranking.

Therefore, due to the fact that the relay’s output fell listed below the specified 12-volt value, the ECU disabled the relay’s power feed circuit after ~ 2 seconds, and set code P2100, i m sorry implicated the throttle manage actuator"s manage circuit(s). However, code P2100 is one amongst many password that are erased immediately when the ignition is turned off, therefore if girlfriend cannot regulate to record it in the two secs you have actually available, you won’t recognize it was ever before set.

To placed the chaotic switching in between polarities into perspective, take into consideration the known-good map of the same function on a chrischona2015.orgparable vehicle below-


Image source: https://www.searchautoparts.chrischona2015.org/sites/default/files/images/FIG10%20copy.png

In this capture, the green trace to represent the inactive, however stable circuit ~ above the accelerator actuator, when the yellow map shows plainly defined steps in the current that the ECU is making use of to nearby the accelerator plate. If the throttle were gift opened, the photo would it is in inverted; the yellow trace would be stable, while the environment-friendly trace would show even, plainly defined steps.

So, given that Jeep does not publish some fault setting parameters, exactly how do you understand if girlfriend are dealing with a straightforward wiring issue, or with chrischona2015.orgponent failures, but more to the point, just how do friend test chrischona2015.orgponents to dominance out or check chrischona2015.orgponent failure(s)? Well, at this allude it help if you have the right to think creatively, or just occur to recognize that ASD relay failure is the many chrischona2015.orgmon cause of no-start conditions on Jeeps. Below are some fast tests you deserve to run to test the relay f you don’t very own a specialty relay experimentation tool-

Test circuits under load



This is wherein sealed beam headlights shine together diagnostic aids due to the fact that where ASD relays space involved, over there is no point in trial and error either the ASD relays’ power feed circuit, or the outputs causing the accelerator actuator v a digital multimeter. While a multimeter might show a reading of 12 volts, a multimeter walk not fill the circuit, so you won"t understand whether the circuits under test break down under their rated loads. Through a headlight, on the various other hand, you load the circuit properly.

So below is a simple trick: attach one terminal of one old sealed beam to the ASD relays’ power feed circuit in ~ the relay, and also connect the other terminal ~ above the headlight chrischona2015.orge a great grounding point. If the circuit is good and the ECU it is provided 12 volts to the circuit, the headlight will certainly glow brightly. If the does not, or does no light up in ~ all, there are three possibilities to consider, this being-

a trouble with the ECUa rest in the circuitan abnormal resistance in the circuit the consumes inordinate amounts of current.

If the power feed circuit is good, reconnect the ASD relay, and repeat the check on every one of the ASD relay"s outputs using the headlight to fill the circuits you space testing. In the instance of the difficulty Jeep, among the relays’ outputs resulting in the accelerator actuator only controlled to make the headlight glow dimly, thus identifying the ASD relay as the problem*, which was evidenced by the chaotic switching between the circuits.

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*Note that a typical problem through these relays involves scorched internal contacts. Also though worn or pitted contacts may severely limit current flow v the relay, this will certainly not necessarily reason the relay to heat up noticeably, which defines why the three young chrischona2015.orgs’ thermal imager walk not disclose the problem when castle looked for hot spots caused by brief circuits and/or abnormally high resistances. 

In this case, the solve was simple: an OEM-equivalent relay to be obtained and installed, and also the Jeep started right up ~ above the an initial attempt. A succeeding test drive v a scan tool linked showed no new issues, and also no brand-new codes to be stored, which ruled out lingering or incipient troubles in various other parts/chrischona2015.orgponents the the vehicles’ beginning circuits and also electronic throttle regulate system, which pipeline us with this-


Although no-start problems on Jeeps have the right to sometimes it is in tricky and also time-consuming to diagnose and also resolve because particular repair and also service details is chrischona2015.orgplicated to find, that is not impossible to solve these kinds of worries with some simple tools and a good measure of an innovative thinking. 

The cheat to addressing these kinds of issues is chrischona2015.orge remember that the ASD relay on a Jeep lies in ~ the love of the start-up logic, and also as such, numerous problems stem straight from this relay if it does not job-related as to plan or designed. In short, if you resolve the relay, girlfriend usually deal with the no-start condition- it’s as simple as that.